Realistically, I’ve never heard a single person claim that slavery should be legal in any form. I’m sure they exist somewhere, but I’ve never encountered them online or in print, much less in real life.
On the other hand, one constantly sees people claiming that racism is about total social power and authority, such that one cannot be racist towards a group that is dominant. Conversely, one cannot be racist if one is a member of a weak group—or at most it is a sort of harmless theoretical possibility with no real world harm.
Yes, it’s fucktarded, but it’s still a surprisingly prevalent view, particularly amongst academics in grievance studies fields.
As with so many dogmas of American political ideology, what works in theory with a white black dichotomy, if you really really want to believe, makes no sense when Asians, Middle Easterners, and other groups are thrown in the mix. At that point all you can try is some sort of bizarre argument that minority A oppressing minority B is, in some convoluted way, to be understood with one’s inner eye as actually the fault of white man C.