An inscription inside the Jefferon memorial says: --- God who gave us life gave us Liberty. Can the liberties of a nation be secure when we have removed a conviction that these liberties are the gift of God? Indeed I tremble for my country when I reflect that God is just, that his justice cannot sleep forever. Commerce between master and slave is depotism. Nothing is more certainly written in the book of fate than that these people are to be free establish the law for educating the common people. This is the business of the state to effect and on a general plan. ---- Would Jefferson have said that? He was a slave owner himself.
The quote isn't some black-and-white assertion against slavery. Thomas Jefferson had complex and evolving relationships with slaves. He owned lots of them (inherited some 135 of them), had a romantic relationship with one of them after his wife died (including kids), waived various fees, and was the key politician who banned importation of new slaves and then slavery itself in numerous states.
It's just wrong to assume that a politician in the late 18th century should have behaved and acted like a radical social justice warrior in the 21st century. There is no contradiction between Jefferson's life and the inscription and Jefferson was an amazing politician and president who has improved the U.S. society dramatically.