This has come up repeatedly on this board. @Reality Check in particular has been fascinated by the subject but I've seen it from more than a dozen of you in, what, a week?
I won't copy and paste this full article, but this is a comprehensive explanation for understanding that "Black on Black crime" is a white supremacist talking point. When you bring up "Black on Black crime", you think you're bringing up a good point maybe, but what you are saying is "I am a mouthpiece for the KKK.