Historically there has been a long and thriving slave trade in Africa long before the white man ever hit the beach there. When the white man did hit the beach in Africa black slave traders were ready, willing and able to bring all the black slaves to the beach that could be carried off for a price.
I do not believe there were any, or at least not very many, whites who reached the beach in Africa that had to go into the bush, capture, contain and transport black slaves to the boats.
What responsibility to blacks have for the slave trade and what should be their own punishment and reparation and to whom?
This is about as stupid a suggestion that anyone living today is guilty of anything or owes anyone anything with regards to slavery or any other mistreatment of the past.
All blm is, is another political hack that should STFU and generally just go to hell.
Only when Europeans began to a dive military supremacy did slavery shift from of Europeans, to by Europeans, and as you note, generally second-hand. Where first hand most cases were of slave holders after slaves were freed, or of retained slaves.