TL;DR: Black lives matter because all lives matter. We need to act more like our lives matter for people to believe it, w/o the Marxist message of BLM.
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Black lives don't matter.
They don't.
We (as a whole, at least in the media) purport ourselves this way. We kill each other and others at higher rates than everyone else. We commit our own genocide from accepting abirtion clinics. We intoxicate and overdose ourselves. We claim the name of Christ (or some god) and live like the devil. Many of us refuse to be educated, especially in history. Heck, we don't even make ourselves look presentable most of the time (there is a difference between an urban or ethnic style and just plain unkempt).
If we can't show ourselves the respect that we should allow ourselves, what makes us think others will.
*I know that Blacks as a whole have gotten way better over the past centuries, and we are, in general more educated than in days past. But if you look around, it seems like you give us the word and we act like rampaging animals, and I'm sick of seeing it while hearing "black lives matter."