I know that pretending to care about stuff to rhetorically buttress one's politics is an Everybody Does It thing, but "what about black on black violence?" is a particularly disingenuous and morally grody example.
White people bringing it up in the context of a discussion of police violence are never, never, never doing so because they actually give a shit about the victims or the affected communities in such cases. They are not searching for ways to alleviate the problem, they are not offering their help or even their sympathy. The entire point is to blame all the suffering of black people on their own moral deficiencies and dismiss any complaints about treatment by the police (and by proxy the white majority) as distractions and reverse racism, possibly stirred up by outsiders and opportunists.
Concern trolling should be old news to me by now, but it rustles me when I bother to think about it.