The primary point, and the ONLY one that matters, is that by selling, buying, trading or owning another human being, you have taken away their AGENCY.
This is fundamentally wrong. Agency is the most basic of human rights, the right to self-determination, and when you have stolen this from someone, you cannot ever claim that anything thereafter is in any way beneficial. It is not your right to say. You stole their destiny, their right to choose for themselves the path they would take, and that is inherently to their detriment. This is not negotiable.
And secondly, the act of claiming any benefit to they themselves, resulting from having enslaved Africans, by its very nature requires an ethnocentric viewpoint; i.e., the notion that a Western, “civilized” life is necessarily better or preferable or to be desired over any other way of life.
This is an entirely subjective determination, and not one anyone can ever make for someone else.”Valuable” skills are only that within one specific value system, which in turn is only one among many of comparable subjective value.