https://www.believemypain.com/
Years ago I posted a study on here that came to the “same” conclusion. Which is, when asked, black people believe they don’t receive equal pain management, despite no medical difference in diagnosis. The absurdity is unreal.
I don't doubt that slavery produces very good value in the short term. If it didn't, it wouldn't have been practiced by every society in human history until about 150 years ago.
The problem is that you can't free slaves without them becoming a permanent liability. They'll never, ever forgive you no matter what you do for them. Therefore the only real solution is extreme brutality. Castration, execution, extermination. But I'm morally against those things, so my only option would be to not have slaves in the first place.