Why do blacks hate slavery?

This may sound like a stupid question.

Yet I'm wondering why do they hate slavery,
after all if it weren't for slavery in the U.S.A,no blacks or hardly any would be in my country today...

Never say the African American could come to the country because of slavery. That was abduction full of violence and murder.
Fine.  If you don't like that, go back to wherever your ancestors came from and migrate properly if it'll make you feel better.