“When it comes to slavery being evil, I agree with you.”
I’m always curious whether that makes George Washington and a lot of other Founders evil. And since London issued two emancipation proclamations during the Revolution whether the wrong side won, judging by 1860 Republican standards. Maybe doubly so, since the Revolution was a war of secession from the United Kingdom and Lincoln’s argument against that was the same as George III.
It is far more difficult to root out corporate sin, and far more difficult to address the individual culpability for that corporate sin. Likewise, the understanding of the violation of human dignity inherent in slavery came to be better understood through the time of the Renaissance.
It was Bartolome de las Casas who articulated a position against slavery in the 16th Century (first only against enslaving the Indians, then later he developed his view to be against the enslavement of anyone, including Africans). Think of the social sins of our own time (including but not limited to abortion, wages that don't match a living wage, environmental destruction, treatment of migrants)—not everyone is equally capable of changing them, and not everyone agrees on the particular solution. For that matter, not everyone even agrees on what the problem is.
In the same way, culpability shifts with understanding. Slavery was always objectively evil... however, it was not always understood to be so, therefore someone in the 14th Century is less culpable for their participation in societal structures that foster and depend on slavery than someone in the 16th, someone in the 16th less than one in the mid-19th, someone in the mid-19th Century less than someone today.
My whole point in bringing up the Founding Fathers at all was to point out the absurdity of the black-and-white thinking on the issue of secession and how slavery ties into it—I did not expect an actual answer to what I understand to be a difficult question, particularly read through a modern lens. Both in the Revolution and the Civil War, slavery was an issue, but not the only issue.