It was a unique western invention (Papal doctrines of "Discovery"), that dehumanized the African slaves, in a way that Islam did not. Only 10% of those loaded on the ships in West Africa, even made it to the New World alive, because of the unthinkably awful conditions that they traveled under, as I understand it. Because these victims weren't valued as people - these loses were considered acceptable. Since those that survived were so valuable.
Neither of the traditions of enslavement (of war prisoners) in West Africa, nor in the Islamic world involved this kind of dehumanizing treatment. It's wrong whenever and wherever it's practiced. But the scope and the scale and the dehumanization in the Transatlantic slave trade have no modern precedents.
That was my point. There's a politicized and revisionist effort afoot to minimize and normalize what occurred in the New World, Europe and Africa, to Africans. I object to it.