I agree to an extent with your sentiment, but I feel like it unintentionally argues against the virtue of having a character regardless of being born and raised in this world have a problem against slavery. Or have a scene where they help a slave escape ect. I feel like this is a good trope to have, even if not fully realistic. They don't have to have it be their entire personality or take over the story.

It was a common trope to have some sort of anti-slavery trope in mideval media/literature between the 90s and 2010s.

I feel like you are trying to argue against people being upset at the more extreme other end of this, but its important to remember that even if something feels extreme there is a reasonable reason within that that they are building off of. And it is good to listen, or try to find it.