Mount Vernon (George Washington’s estate) does a pretty good job of exploring that mind set without ever justifying slavery or down playing the horrific nature of it. American society was built on slavery, so the people born at the top and benefiting from it would have no reason to question, is this right, because if it’s not then all the people who raised me were evil and that can’t be true.
There is a lot of similarities between the slave owner class of the civil war and the “capitalist elite” of today. “Why ban slavery if I’m not enslaved and could maybe one day own a slave” is about like “why tax billionaires if I don’t need the government and I might one day be a billionaire?”.