It is, actually, since you as a white person are in no way qualified to say "who is black", which is the entire premise of the term.
It's also why goyim should stop trying to lecture others about "who is a jew", or why hets should stay in their lane with the "is it gay" nonsense. You are still fundamentally erasing the agency of those groups by denying them the right to define themselves.
And this, dear readers, is a perfect example of brocialism in action. Social justice is not an end in of itself, it's a cudgel that they use to bully others with.