All lives matter is a way of shutting up activists and is a really ignorant perspective. black lives are the ones being threatened daily on the streets and so that's why we are focusing on black lives--because for hundreds of years they have been treated like they don't. stop being defensive and start listening!
Yes, all lives matter, but right now we're focusing on the black ones. if a child gets a cut, are you going to give a bandaid to all the children or just the one that got hurt?
All lives should matter. In practice, however, many lives are treated as though they do not matter as much as others. That is why the Black Lives Matter movement exists.
Black Lives Matter! About the "all lives matter" response: The principle is right and understandable, but the phrase is so often used by white nationalists to shut down any black movement that you associate yourself with them. Just like here in germany it is fascist to use words like Überfremdung (over-foreignization), Umvolkung (assimilation of germans) or Lügenpresse (lying press), because they are strongly associated with the third reich. It's not even about those things being right or wrong any longer, it's that they were used as propaganda by nazis, or in this case are used by white supremacists.
Post scriptum: When I was little I heard the phrase "Jedem das Seine" ("to each their own"? I think) and thought that I liked it. It sounds pretty egalitarian, right? Then I grew up and learned that it's the phrase on the gates to the KZ in Auschwitz. I kinda get a queasy feeling each time I hear or read it now (thankfully *very* seldomly). Now consider how condescending and dismissive it must sound to a black person (I imagine, and please correct me if I'm wrong) to reply to blm with alm. Even if you mean it in a sense of inclusion and equality for all.