One of our best hopes for diminishing racism to non-problematic levels is recognizing our common humanity.

Of course anyone can be racially bigoted--the question is really about whether "racism" is synonymous with "racial bigotry" or whether it necessarily also requires the highest levels of institutional power in the country. We could make words mean anything we want, and there's an argument from usage for either perspective, so in a sense we have a choice. Neither way is flat out wrong historically.

I agree with most everything you say--but I think our choice of terminology still matters. When we say, "Only whites can be racist," we divide and tribalize rather than unify as humans-with-some-superficial-differences.

Words have power to shame, and to divide, and to unify, as well as to inform. You're right that the error, if any, in information from "only whites can be racist" is small enough to neglect, at least on the level of American society as a whole. Who cares, indeed, if blacks can be racist? The impact is almost negligibly small compared to the sum total of racism from whites.

But when trying to solve our problems, the error in sewing division when unity is needed is substantial.

So it matters.