I like the "Black Lives Matter" movement. I also like the "Black Lives Matter" name, as long as it's understood that "Black Lives" is intended as a convenient shorthand for "Whichever Lives Are Most Affected By Police Brutality At The Moment". I don't like that so many adherents of the "Black Lives Matter" movement object to the "All Lives Matter!" meme and call it racist, because this tells me that they're definitely taking the "Black Lives" part the wrong way.
Well, different people understand it in different ways. Some are horrible people who understand it in the worst way. Others are great people who understand it in the best way. The entire group is willing to sacrifice clarity and a clear definition, in favor of something sufficiently vague to band together a collective action who overlap on certain dimensions.
I think for that reason though, trying to debate the definition or how it's understood is pointless. Sadly. I don't blame people who think it's a worthy cause anyway, maybe they are right. I personally can't stand associating with movements where the direction isn't clear, but that's just me.