1/ What if "slavery" was just called something else? Blacks worked fewer hours per year than free white farmers, had better nutrition as inferred from height (blacks are actually slightly shorter than whites today), and their life expectancy ratio was roughly the same today.

2/ And their literacy rate was ~20%, higher than most of the world. Certainly higher than black africa

When you actually break down what data there is on slavery, and how most former slaves who had a choice after the civil war actually chose to stay on with their former...

3/ masters, how horrible is this really compared to how most of the world actually was at the time? In Russia, you weren't a "slave", you were a "serf", though every metric of human development was worse than a US slave.

4/ So I think a lot of this comes down to the word "slave" and the emotional connotation injected into it. People wonder how those in 1840 could be so sanguine about SLAVERY. Probably because the reality was far more mundane than abolitionist propaganda portrayed it.

5/ This isn't to say it's good or ideal. BUT (yes, BUT, as in there's something else to consider) being a negro slave was not a bad place to be in in the global context of the time.