The meaning of any political statement depends on the context in which it is said. The slogan "Black Lives Matter" began after videos circulated showing police killing black people, sometimes for trivial offenses. In that context, it clearly means not that black lives matter more than others or that white people’s lives don’t matter, but that black lives matter just as much as others. That is the point that needed to be made in response to those videos. "Black lives matter" is therefore not a racist slogan—just the opposite.