On the surface "Black lives matter" sounds innocuous. Only a racist would assert that black lives don't matter. But it is an implicit accusation: "Black lives matter even if you don't think so." It is a way of insinuating that everyone is a racist unless they fall in line with the movement.
But what if you say, “ALL Black Lives Matter”, and not just the ones killed by white police, and who are not “Down Wit Da Shtruggle”?