> Almost 100% of the African-American population
Well, no. Africans (before they were captured and sold to the Dutch slave traders) had slaves. A lot of Africans were sold into slavery by other Africans, the ones they lost tribal wars to. Slavery was very well known in Africa, just as it was everywhere else in the world basically from the moment civilization was created.
Like most things, people were ok with it happening to others and only had an issue when it happened to them.
The idea that all slavery is wrong is a far more modern idea. Unlike the OP I do not present that as a bad thing.