bfl
The problem with WW's statement here is that slavery in America was racist. It had to be racist in a nation founded on "all men are created equal."
In a society like most thru history where there are many shades of privilege, extending from the King down through the nobles to the middle and lower classes and eventually to various categories of slaves, at some point the "line" between "freedom" and "slavery" is crossed, but which side of the line you are on makes little difference in your life.
In a society like ours, where "all men are free," there has to be some (seemingly) logical reason why some men obviously aren't free.
The answer was racism. Explained it perfectly logically, if you accept the premise. Black people are enslaved because they aren't really men.
So one can continue to believe in both slavery and the Declaration of Independence without one's head exploding.
Slavery in most parts of the world and down through history hasn't been particularly racist in character. Slavery in the New World and especially in American certainly was.