See, that's the thing. All lives do matter. But it appears that in the US (and here to an extent), black lives don't. Why do you think the protests sprung up? Its because police (not all obviously) felt they could shoot/kill or choke/abuse black suspects with impunity. And, up until the advent of cell phones, they probably did. There are countless examples of black men being killed due to trigger happy cops or ones that don't follow the correct procedures. I'm a white man, and 20 years ago I would have said most of these types of allegations about the treatment of blacks was bullshit. Now, we've seen what happens. It isn't an exaggeration. They are treated differently, and with deadly consequences.
Remember that kid in Cleveland (I think), who was playing with a toy gun? The cops arrived on the scene and SHOT HIM DEAD in seconds. There was no chance to de-escalate or even tell him to drop the weapon. Just BANG. Would the cops have rolled that aggressively on a white child? Odds are no.
Maybe the slogan should be Black Lives Matter As Well (BLMAW)! Because in many parts of American society, they are disposable people. You look at places like Flint, MI, where the lead in pipes has poisoned hundreds of mostly black children. It's a problem they knew about for years, and did nothing (even to this day).
So, yes all lives matter. But that isn't what is happening in the US, and if you look at how we treat the first nations, up here in Canada.
Anytime someone spouts this "All Lives Matter" bullshit is totally missing the point. BLM is not about the supremacy of blacks, or them wanting special treatment. No, they want to be treated like any other citizen. They don't want to be gunned down or assaulted by police just because they're black. So, it isn't race baiting.