"like a good person in the pre-civil war era" is so darkly hialrious to me. I run in old setting, Mystara, where two biggest empires have legal slavery and are also bittere rivals. One, Thyatis, is based off Roman Empire and biggest hurdle to ending slavery is that whenever you try to argue against it, Thyatians point at other empire, Alphatia, and it's "pre civil-war south style slavery" and argue that next to this their (a.k.a. Roman) style of slavery is very humane.
And I still made it very clear that if any of my players try buying slaves, no god will save them from my wrath.