I don't think this is really controversial. Racism, which is to say a kind of race essentialism, is a product of slavery and the desire to be able to justify it. And later on, that idea really dovetailed with scientific racism which was in some ways even nastier, imo, even though it really came into its own after slavery was abolished.
But it's not a fundamentally different, or worse, process than the way other groups justify their domination of others. You can hear some pretty awful things by Africans about why other Africans from different tribes deserve to be lower in the social hierarchy.Or go to India - there is some pretty awful stuff of the same kind going on in their politics today, and it also could be traced back to historic migrations and invasions which have nothing to do with Europeans.
I think what gets people's back up is partly that it's treated so differently from the same process in other places, and also the fact that it was dismantled as a legal system or acceptable ideology in a way that hadn't happened anywhere else.
But also the way that has been turned on its head with this very weird narrative around "whiteness" as a kind of reified thing, and actually creating a new kind of race essentialism that simply has a different hierarchy - and those white people who don't accept this are racists.
I think it's rather had the effect of setting back work done around racism by decades. To the point that people who really grew up with no I'll feelings around race at all are finding themselves thinking about people more and more as members of a race, and often feeling angry in an unspecified way.