It seems to me that "Black people ran the slave trade" is not so much (should not be) "tu quoque", but rather a reminder that "Whites didn't enslave blacks"..... more accurately, "Whites didn't do anything to stop blacks from enslaving other blacks.. and more so contributed to the slave trade industry by increasing demand dramatically".
The difference is slight, but important to many... it's one thing to sit idly by, another to participate, and completely another to be the actual impetus / aggressor
Almost every part of this is either a distortion or a lie outright. Your casual use of "Black" and "White" as primary signifiers is anachronistic and obsfuscating. You claim that "Whites did not enslave blacks", which is
demonstrably untrue. You claim that the only "White" involvement was by "increasing demand dramatically", which - considering that the entire Transatlantic trade was dependent on European and Middle Eastern markets (both ends), prisons, police, warehouses, ships, currency, firearms, purchasers, and labor - is a bit like claiming claiming that Amazon is only a catalogue publisher. You seem to claim that "Whites" were not aggressors in all of this, which is wrong to the point of bizarre. There was no such thing as a "White", not even in the popular imagination, until active participation in and endorsement of slavery on an institutional level obliged European and American legal entities to find an excuse to justify why some subjects of the Crown had basic human rights and others didn't, specifically because they had built a planned economy based on the premise of a constantly expanding slave population.
Slavery did not passively happen to the various Christian and Muslim powers of this time period. Rather, they actively and violently pursued this practice, built almost all its infrastructure, and pocketed most of its bounty. By the time the system started to collapse, the Portuguese had formed entire colonial states on the African coast just so they could cut Dahomean middlemen
out of that market, capturing and selling slaves directly to maximize profit in a business that was starting to become less lucrative. That's to say nothing of those enslaved or re-enslaved
in Europe and the Americas, often mere months after their birth. None of this excuses the actions of the kings of the Dahomean, Aro, and Songhay, and other West African empires. They too did terrible, terrible things, and their regimes were no less dependent on the maintenance of a permanent slave caste. But observing that does not or should not lessen the responsibility European and American powers have for their own freely taken and violently defended actions.