I was coming here to say what several people have already said: saying "Black Lives Matter" is not saying "ONLY Black Lives Matter" or that "Black Lives Matter MORE" ... if that's what you think, the entire point of the saying went so far over your head it's not worth debating.
Agreed. "All Lives Matter" is sinister in that it 1) Makes it seem as though BLM believes that white lives don't matter and 2) Completely misses the point of the movement.
Every life does matter, but it's only black people who die and have society at large ignore their deaths or dismiss it as "He probably deserved it." Innocent white people get killed by police, but when it happens the officer doesn't get letters thanking him for killing white people and a defense fund set up by supporters.