I agree with Azizi there about playing games about one atrocity being worse than another. It's a way of diverting attention from the real issues.

It's right to remind people that there are and have been other evils in the world as well as the particular one people focus there attention on, but that shouldn't be used as a way of somehow shifting the blame.

And blame isn't what it shoudl be about. The primary object should be to try to identify what are the characteristics of the the system we live in which have led to these historic crimes by people with whom we share an enormous amount, in societies which in many ways were very similar to ours.

History doesn't repeat itself precisely, but variants on the same theme recur.   Chattel slavery founded on brute force and arbitrary "racial" distinctions probably won't come again in that form, but the the continuing economic and political system which invented it is capable of coming up with more efficient ways of turning people into property and stealing their freedom.

Chattel slavery (only one of a number of different varants of slavery, though arguably the most grotesquely dehumanising for both parties) has a major disadvantage that you can't just lay off workers when you don't need them, and pick them up again when you do, if they have managed to survive. That's a main reason why as a system it is no longer a major player.

But if we tell ourselves that this means that slavery of one sort or another is dead and gone for ever we need a wake up call.