Tbf FLT, I can see what is winding up the guys and your point as well. Of course all lives should matter equally, but the slogan black lives matter points at the issue that black American lives don't appear to matter. At least nowhere near as much as the majority population of white Americans. It's the focus that is the requirement. In a similar way, if you remember when the journalist Owen Jones walked out of a Sky News programme on the Orlando shootings, and he wanted the presenter and other correspondent to recognise that it was a gay-hatred motivated crime. They were talking about people being killed, and rightly so, but they failed to recognise the importance that it was gay-hatred orientated. It was the focus they lacked.
I'm not criticising, just making the observation.