But we also know that the Republican party and Democratic parties of the civil war era are not the same as they are now.
I mean, I guess you could argue that it was part of the culture to have slaves and treat them as livestock, but we also know there were many people, white and black that were against it while it was happening legally. Some people were okay believing blacks were sub-human and many people were not... in that regard, you can't really compare it to livestock as I don't think you had as many vegans crying about cows being enslaved as you did humans.
Even in the 17 and 1800s it would take a special kind of asshole to believe a human was less than yourself because they had darker skin. Many people knew it was wrong then too.