I don't have many deep assumptions. I try to figure out what is the case, on the basis of the best evidence and argumentation available. I'm always open to new arguments. So my only real assumption is that you should show your work if you want me to believe you.

(1) I didn't say racism was identical to tribalism. I said tribalism causes racism. Specifically, people can identify their race as "their tribe", and can identify members of another race as another tribe. They can absolutely stop doing this--switch who they identify with, and then maybe they won't be explicitly racist any more. (Implicit bias takes longer to switch precisely because it's non-declarative in nature.)

(2) Justifying slavery (but also colonialism) was a key reason why racism was advocated. I'm a bit less certain about race, because at the time biological classification was a hot topic, but of course the answer for race had to align with the justifications for slavery and colonialism. But anyway, why is this relevant now?

(3) I know you have stated repeatedly that race reductionism is designed to serve upper classes or Wall Street or whatever. But I haven't yet seen a compelling argument from you, so I withhold judgment. I am skeptical because the upper classes seem to rapidly find a way to make almost everything come out in their favor--even populism (c.f. Trump)! I am also skeptical because the financial elites are among the most demonized group by the intellectual elites in the humanities, which suggests to me that there is little unity of purpose here. But this is just a suspicion; obviously it would not stand up to clear evidence of linkage, say, between financial interests whose natural inclinations would be hostile to race reductionism, and those promoting race reductionism, because (presumably) they understood that the resulting culture war would occupy those who would otherwise oppose the financial interests. Even so, many people who support race reductionism also are extremely critical of capitalism, so it would be a very dangerous game to play--anyone supporting this would have to be quite sure that the effort would ultimately fail, or the elites would be jeopardized. (Then again, people often make stupid gambles and lose, so this isn't a very compelling counterargument.)