I'm uncertain why, someone else explained some good thoughts here and was similarly down voted. I suspect a lack of empathy is part of why this is going poorly, most people online I interact with seem to have deeply impaired empathy.
We're talking about an entirely different, period and place specific morality, with an entire society functioning around that framework. Objectively bad and the idea that all these people belong in Hell is absurd.
Obviously slavery is bad, but that's only because we've come to understand these ideas, but on the same token, obviously slavery is bad for prisoners, but the US allows this, and many people even know about this and do not care - hopefully future generations don't judge all of us as deserving Hell.
This country has elected an actual literal racist Bigfoot who is moving the country towards a white Christian nationalism, hopefully we are all not judged as evil racist nationalists, hopefully in the future, the entire American populace is not judged to belong in Hell.
Most people, of all eras adapt to what is normalized, including morally. I promise you and I, and everyone you know would operate from a different normalized moral framework, the only difference is I understand this.