Personally, I think that the United States has systematically mistreated black people for centuries and not acknowledging that such problems still exist is willful ignorance.

> Personally, I think saying only one group matters tends to read as supremacist.

I agree wholeheartedly. Had the messages in question said "Only black lives matter," I would support crossing them out.

But I don't understand how crossing out "Black lives matter" is supposed to be interpreted as "Yes, and other lives matter too" instead of the straightforward "No, black lives don't matter."