Back in the day when slavery was a common thing, it was either them or the other side that was going to be slaves. Don't tell me that if the shoe was in the other foot, the blacks would have made whites their slaves. That's how the world was back them. If you don't eat them, they'll you eat you first.
Nevertheless, slavery is inhumane no matter who it's done to (unless they want to be a slave). And, at least for Jews, who were slaves, we became stronger and better for it. For African Americans, stronger, but for many, not necessarily better for it.
Finally, when Lincoln outlawed slavery, there was an option the table to pay them and have them go back to Africa...but it didn't pass because of one vote due to the expenses. (well look today as a result of not humanely paying wages to the slaves and their families and not sending them back.)