Adapted from information found on wallbuilders.com

The majority of the Founders opposed slavery.  There is evidence that James Madison, Thomas Jefferson, and John Rutledge, at one time, favored slavery. Jefferson, Writings, Vol. I, p. 28, from his autobiography; see also James Madison, The Papers of James Madison (Washington: Langtree and O'Sullivan, 1840), Vol. III, p. 1395, August 22, 1787; see also James Madison, The Writings of James Madison, Gaillard Hunt, editor, (New York: G. P. Putnam's Sons, 1910), Vol. IX, p. 2, to Robert Walsh on November 27, 1819.

The Founding Fathers planted the first seeds for the recognition of black equality and for the eventual end of slavery.

Jefferson introduced a bill designed to end slavery, Jefferson, Writings, Vol. I, p. 4.

There is a logical correlation between American slavery and evolutionary theory: Both are effects produced by the same cause, namely, disregarding the Bible when it applies to secular topics such as politics and science. But some might protest that American slavery preceded Charles Darwin’s influence—so how can evolution and slavery be related? ~ http://www.icr.org/article/7236/

Darwin’s own words proposed a theory that all men were not equal, and Darwinism’s promoters used preexisting racist attitudes to help sell Darwin’s natural selection theory, teaching that darker-skinned humans were less evolved than lighter-skinned humans:
 No rational man, cognizant of the facts, believes that the average Negro is the equal, still less the superior, of the white man.8
 As shown by this quote from evolutionist hero Thomas Huxley, “Darwin’s bulldog,” ethnic racism clearly predates the influence of Darwin’s natural selection theory.5 Yet Darwin’s theory and American slavery practices can both be traced to the same kind of humanistic thinking—closed-Bible thinking about secular topics—called “rationalism” or “free-thinking.” Led by leaders of the deism movement, rationalism experienced a popular revival in the 1700s and early 1800s. Deists were closed-Bible creationists, precursors of the Intelligent Design Movement.9 Deists actively and passively rejected the biblical creation teachings of Genesis, including teachings on human origins, ethnic origins, and geologic history.~ http://www.icr.org/article/7236/

In deism-grounded science, the earth was imagined to be millions of years old (or older). Similarly, deists rejected the family history of Adam’s race recorded in Genesis, teaching that the words of the Bible were a prescientific Semitic myth (unfit for the enlightened minds of reason-ruled intellectuals). Thus, this mindset that rejected Genesis history was already becoming popular, thanks to Dr. Hutton and his ilk, long before the U.S. Constitution was ratified! ~ http://www.icr.org/article/7236/

Many Founding Fathers never had slaves.
[M]y opinion against it [slavery] has always been known... [N]ever in my life did I own a slave. ~ John Adams, The Works of John Adams, Second President of the United States, Charles Francis Adams, editor (Boston: Little, Brown, and Company, 1854), Vol. IX, pp. 92-93, to George Churchman and Jacob Lindley on January 24, 1801.

Many Founding Fathers freed their slaves, for example:
George Washington
John Dickinson
Caesar Rodney
William Livingston
George Wythe
John Randolph of Roanoke

In 1774, Benjamin Franklin and Benjamin Rush founded America's first anti-slavery society.
John Jay was president of a similar society in New York. 
Other prominent Founding Fathers who were members of societies for ending slavery included Richard Bassett, James Madison, James Monroe, Bushrod Washington, Charles Carroll, William Few, John Marshall, Richard Stockton, Zephaniah Swift, and many more.
Based in part on the efforts of these Founders, Pennsylvania and Massachusetts began abolishing slavery in 1780; Connecticut and Rhode Island did so in 1784; Vermont in 1786; New Hampshire in 1792; New York in 1799; and New Jersey did so in 1804.

Rufus King, signer of the Constitution authored a Congressional Act, that George Washington signed into law, that prohibited slavery in Ohio, Indiana, Illinois, Michigan, Wisconsin, and Iowa. ~ Acts Passed at a Congress of the United States of America (Hartford: Hudson and Goodwin, 1791), p. 104, August 7, 1789. The Constitutions of the United States (Trenton: Moore and Lake, 1813), p. 366, "An Ordinance for the Government of the Territory of the United States Northwest of the River Ohio," Article VI.

I abhor slavery. I was born in a country where slavery had been established by British Kings and Parliaments as well as by the laws of the country ages before my existence.... In former days there was no combating the prejudices of men supported by interest; the day, I hope, is approaching when, from principles of gratitude as well as justice, every man will strive to be foremost in showing his readiness to comply with the Golden Rule ["do to others as you would have them do to you" Matthew 7:12]. President of Congress Henry Laurens, Frank Moore, Materials for History Printed From Original Manuscripts, the Correspondence of Henry Laurens of South Carolina (New York: Zenger Club, 1861), p. 20, to John Laurens on August 14, 1776.

Prior to the great Revolution, the great majority... of our people had been so long accustomed to the practice and convenience of having slaves that very few among them even doubted the propriety and rectitude of it. ~ John Jay, The Correspondence and Public Papers of John Jay, Henry P. Johnston, editor (New York: G. P. Putnam's Sons, 1891), Vol. III, p. 342, to the English Anti-Slavery Society in June 1788.

He [King George III] has waged cruel war against human nature itself, violating its most sacred rights of life and liberty in the persons of a distant people who never offended him, captivating and carrying them into slavery in another hemisphere or to incur miserable death in their transportation thither.... Determined to keep open a market where men should be bought and sold, he has prostituted his negative for suppressing every legislative attempt to prohibit or to restrain this execrable commerce [that is, he has opposed efforts to prohibit the slave trade]. 3
Benjamin Franklin, in a 1773 letter to Dean Woodward, confirmed that whenever the Americans had attempted to end slavery, the British government had indeed thwarted those attempts. Franklin explained that... ~ Thomas Jefferson, The Writings of Thomas Jefferson, Albert Ellery Bergh, editor (Washington, D. C.: Thomas Jefferson Memorial Assoc., 1903), Vol. I, p. 34.

... a disposition to abolish slavery prevails in North America, that many of Pennsylvanians have set their slaves at liberty, and that even the Virginia Assembly have petitioned the King for permission to make a law for preventing the importation of more into that colony. This request, however, will probably not be granted as their former laws of that kind have always been repealed. Benjamin Franklin, The Works of Benjamin Franklin, Jared Sparks, editor (Boston: Tappan, Whittemore, and Mason, 1839), Vol. VIII, p. 42, to the Rev. Dean Woodward on April 10, 1773.

The inconsistency of the institution of domestic slavery with the principles of the Declaration of Independence was seen and lamented by all the southern patriots of the Revolution; by no one with deeper and more unalterable conviction than by the author of the Declaration himself [Jefferson]. No charge of insincerity or hypocrisy can be fairly laid to their charge. Never from their lips was heard one syllable of attempt to justify the institution of slavery. They universally considered it as a reproach fastened upon them by the unnatural step-mother country [Great Britain] and they saw that before the principles of the Declaration of Independence, slavery, in common with every other mode of oppression, was destined sooner or later to be banished from the earth. Such was the undoubting conviction of Jefferson to his dying day. In the Memoir of His Life, written at the age of seventy-seven, he gave to his countrymen the solemn and emphatic warning that the day was not distant when they must hear and adopt the general emancipation of their slaves. ~ John Quincy Adams, An Oration Delivered Before The Inhabitants Of The Town Of Newburyport at Their Request on the Sixty-First Anniversary of the Declaration of Independence, July 4, 1837 (Newburyport: Charles Whipple, 1837), p. 50.

[E]ven the sacred Scriptures had been quoted to justify this iniquitous traffic. It is true that the Egyptians held the Israelites in bondage for four hundred years,... but... gentlemen cannot forget the consequences that followed: they were delivered by a strong hand and stretched-out arm and it ought to be remembered that the Almighty Power that accomplished their deliverance is the same yesterday, today, and for ever. ~ Elias Boudinot, President of the Continental Congress, The Debates and Proceedings in the Congress of the United States (Washington, D. C.: Gales and Seaton, 1834), First Congress, Second Session, p. 1518, March 22, 1790; see also George Adams Boyd, Elias Boudinot, Patriot and Statesman (Princeton, New Jersey: Princeton University Press, 1952), p. 182.

[W]hy keep alive the question of slavery? It is admitted by all to be a great evil. CHARLES CARROLL, SIGNER OF THE DECLARATION, Kate Mason Rowland, Life and Correspondence of Charles Carroll of Carrollton (New York & London: G. P. Putnam's Sons, 1898), Vol. II, p. 321, to Robert Goodloe Harper, April 23, 1820.

As Congress is now to legislate for our extensive territory lately acquired, I pray to Heaven that they may build up the system of the government on the broad, strong, and sound principles of freedom. Curse not the inhabitants of those regions, and of the United States in general, with a permission to introduce bondage [slavery]. JOHN DICKINSON, SIGNER OF THE CONSTITUTION; GOVERNOR OF PENNSYLVANIA, Charles J. Stille, The Life and Times of John Dickinson (Philadelphia: J. P. Lippincott Company, 1891), p. 324, to George Logan on January 30, 1804.

That men should pray and fight for their own freedom and yet keep others in slavery is certainly acting a very inconsistent, as well as unjust and perhaps impious, part. ~ JOHN JAY, PRESIDENT OF CONTINENTAL CONGRESS, ORIGINAL CHIEF JUSTICE U. S. SUPREME COURT, John Jay, The Life and Times of John Jay, William Jay, editor (New York: J. & S. Harper, 1833), Vol. II, p. 174, to the Rev. Dr. Richard Price on September 27, 1785.

The whole commerce between master and slave is a perpetual exercise of the most boisterous passions, the most unremitting despotism on the one part, and degrading submissions on the other.... And with what execration [curse] should the statesman be loaded, who permitting one half the citizens thus to trample on the rights of the other.... And can the liberties of a nation be thought secure when we have removed their only firm basis, a conviction in the minds of the people that these liberties are of the gift of God? That they are not to be violated but with His wrath? Indeed I tremble for my country when I reflect that God is just; that his justice cannot sleep forever. ~ THOMAS JEFFERSON, Thomas Jefferson, Notes on the State of Virginia (Philadelphia: Matthew Carey, 1794), Query XVIII, pp. 236-237.

Christianity, by introducing into Europe the truest principles of humanity, universal benevolence, and brotherly love, had happily abolished civil slavery. Let us who profess the same religion practice its precepts... by agreeing to this duty. ~ RICHARD HENRY LEE, PRESIDENT OF CONTINENTAL CONGRESS; SIGNER OF THE DECLARATION, Richard Henry Lee, Memoir of the Life of Richard Henry Lee, and His Correspondence With the Most Distinguished Men in America and Europe, Illustrative of Their Characters, and of the American Revolution, Richard Henry Lee, editor (Philadelphia: H. C. Carey and I. Lea, 1825), Vol. I, p. 19, the first speech of Richard Henry Lee in the House of Burgesses of Virginia.

I hope we shall at last, and if it so please God I hope it may be during my life time, see this cursed thing [slavery] taken out.... For my part, whether in a public station or a private capacity, I shall always be prompt to contribute my assistance towards effecting so desirable an event. ~ WILLIAM LIVINGSTON, SIGNER OF THE CONSTITUTION; GOVERNOR OF NEW JERSEY, William Livingston, The Papers of William Livingston, Carl E. Prince, editor (New Brunswick: Rutgers University Press, 1988), Vol. V, p. 358, to James Pemberton on October 20, 1788.

[I]t ought to be considered that national crimes can only be and frequently are punished in this world by national punishments; and that the continuance of the slave-trade, and thus giving it a national sanction and encouragement, ought to be considered as justly exposing us to the displeasure and vengeance of Him who is equally Lord of all and who views with equal eye the poor African slave and his American master. ~ LUTHER MARTIN, DELEGATE AT CONSTITUTIONAL CONVENTION, Luther Martin, The Genuine Information Delivered to the Legislature of the State of Maryland Relative to the Proceedings of the General Convention Lately Held at Philadelphia (Philadelphia: Eleazor Oswald, 1788), p. 57; see also Debates in the Several State Conventions on the Adoption of the Federal Constitution, Jonathan Elliot, editor (Washington: Printed for the Editor, 1836), Vol. I, p. 374.

As much as I value a union of all the States, I would not admit the Southern States into the Union unless they agree to the discontinuance of this disgraceful trade [slavery]. ~ Elliot's Debates (Washington: Printed for the Editor, 1836), Vol. III, pp. 452-454, George Mason, June 15, 1788.

Honored will that State be in the annals of history which shall first abolish this violation of the rights of mankind. ~ JOSEPH REED, REVOLUTIONARY OFFICER; GOVERNOR OF PENNSYLVANIA, William Armor, Lives of the Governors of Pennsylvania (Norwich, Conn.: T. H. Davis & Co., 1874), p. 223.

Domestic slavery is repugnant to the principles of Christianity.... It is rebellion against the authority of a common Father. It is a practical denial of the extent and efficacy of the death of a common Savior. It is an usurpation of the prerogative of the great Sovereign of the universe who has solemnly claimed an exclusive property in the souls of men. ~  BENJAMIN RUSH, SIGNER OF THE DECLARATION, Benjamin Rush, Minutes of the Proceedings of a Convention of Delegates from the Abolition Societies Established in Different Parts of the United States Assembled at Philadelphia (Philadelphia: Zachariah Poulson, 1794), p. 24.

Justice and humanity require it [the end of slavery]-Christianity commands it. Let every benevolent... pray for the glorious period when the last slave who fights for freedom shall be restored to the possession of that inestimable right. ~ NOAH WEBSTER, RESPONSIBLE FOR ARTICLE I, SECTION 8, 8 OF THE CONSTITUTION, Noah Webster, Effect of Slavery on Morals and Industry (Hartford: Hudson and Goodwin, 1793), p. 48.

Slavery, or an absolute and unlimited power in the master over the life and fortune of the slave, is unauthorized by the common law.... The reasons which we sometimes see assigned for the origin and the continuance of slavery appear, when examined to the bottom, to be built upon a false foundation. In the enjoyment of their persons and of their property, the common law protects all. ~ JAMES WILSON, SIGNER OF THE CONSTITUTION; U. S. SUPREME COURT JUSTICE, James Wilson, The Works of the Honorable James Wilson, Bird Wilson, editor (Philadelphia: Lorenzo Press, 1804), Vol. II, p. 488, lecture on "The Natural Rights of Individuals."

[I]t is certainly unlawful to make inroads upon others... and take away their liberty by no better means than superior power. ~ JOHN WITHERSPOON, SIGNER OF THE DECLARATION, John Witherspoon, The Works of John Witherspoon (Edinburgh: J. Ogle, 1815), Vol. VII, p. 81, from "Lectures on Moral Philosophy," Lecture X on Politics.

I would most ardently wish to become a member of it [the anti-slavery society in New York] and... I can safely promise them that neither my tongue, nor my pen, nor purse shall be wanting to promote the abolition of what to me appears so inconsistent with humanity and Christianity.... May the great and the equal Father of the human race, who has expressly declared His abhorrence of oppression, and that He is no respecter of persons, succeed a design so laudably calculated to undo the heavy burdens, to let the oppressed go free, and to break every yoke. ~ William Livingston, regarding the New York anti-slavery society, The Papers of William Livingston, Carl E. Prince, editor (New Brunswick: Rutgers University Press, 1988), Vol. V, p. 255, to the New York Manumission Society on June 26, 1786.

I can only say that there is not a man living who wishes more sincerely than I do to see a plan adopted for the abolition of it [slavery]. ~ George Washington, The Writings of George Washington, John C. Fitzpatrick, editor (Washington, D. C.: Government Printing Office, 1932), Vol. XXVIII, pp. 407-408, to Robert Morris on April 12, 1786.

Many of the white people have been instruments in the hands of God for our good, even such as have held us in captivity, [and] are now pleading our cause with earnestness and zeal. ~ Richard Allen who was freed after his master became a Christian, The Life Experience and Gospel Labors of the Right Rev. Richard Allen (Nashville: Abingdon Press, 1983), p. 73, from his "Address to the People of Color in the United States."

[T]he Constitution allowed Southern States to count three-fifths of their slaves toward the population that would determine numbers of representatives in the federal legislature. This clause is often singled out today as a sign of black dehumanization: they are only three-fifths human. But the provision applied to slaves, not blacks. That meant that free blacks-and there were many, North as well as South-counted the same as whites. More important, the fact that slaves were counted at all was a concession to slave owners. Southerners would have been glad to count their slaves as whole persons. It was the Northerners who did not want them counted, for why should the South be rewarded with more representatives, the more slaves they held? ~ THOMAS WEST, Principles: A Quarterly Review for Teachers of History and Social Science (Claremont, CA: The Claremont Institute Spring/Summer, 1992), Thomas G. West, "Was the American Founding Unjust? The Case of Slavery," p. 5.

These quotes and most of this information taken from wallbuilders.com/LIBissuesArticles.asp?id=122