He is arguing that the post-modernist, Marxist nature of BLM makes it genocidally dangerous.

I don't agree, but that it his argument.

*EDIT TO ADD* I shouldn't speak for Denny here. I think that's his argument. But even if I'm wrong about that, the simple point here is, for political movements that are deranged or fundamentally flawed, you wouldn't need to assert anything about a group to say the movement won't benefit that group. Example: Anti-capitalists aren't saying anything generalizing about Africans when they say capitalism exploits them. They are just saying, capitalism exploits humans, including Africans.