I hear this excuse all the time. It goes like "well Africans were originally enslaved by other Africans so black people in America should be mad at them instead of blaming white people".
Well, there's a lot to unpack. First, yeah, some Africans enslaved other Africans and sold them to European traders BUT not all of the Africans were on board with this (namely the factions who had members of their family abducted and were never able to see them again). What do you think the communities in Africa that went about enslaving others managed to capture and sell off the members of all the other communities leaving only those that partook in slavery left? No, the descendants of communities that were plundered for their people are still present in Africa today.
But to further highlight why this excuse is so unfounded, lets say that there's a human trafficking ring that was busted. Now if you bought someone from that cartel or acted as a middle-man in that trade, they're not off the hook because they didn't capture the people who were trafficked in the first place.