Excerpts from Books and Wikipedia
"Delegates from Georgia and South Carolina, the only states to keep importing slaves from Africa legal after the Revolution, threatened to bolt if the issue so much as came to the floor of the convention. When Gouverneur Morris delivered a thunderous attack on 'a nefarious institution' that he called 'the curse of heaven on the states where it prevailed,' he was only restating a characterization made with increasing frequency in the North since the 1770s. Slavery had been condemned in the new constitutions of Vermont, Pennsylvania, and Massachusetts, and some states were adopting plans of gradual abolition. Gouverneur Morris had already demanded abolishing slavery in his native New York, reasoning that every human being should enjoy the same privileges as every other. Slavery was under attack in many northern states by the late 1780s, for economic reasons as well as the ethical reasons Morris offered. The Society of Friends made opposing slavery a condition of membership, and many Methodist congregations followed suit, but such religious fervor only antagonized many fence-sitters." [Toward Democracy, Kindle Location 9618-9633]