It's not just a hook - black people are oftentimes the testing grounds for unjust programs that expand in scope to engulf other peoples (e.g. the prison industrial complex). The full tag line should be "All lives will matter when Black Lives Matter" because they are at the intersections of so many institutional inequities.
Something I've said for a while is that many "conspiracy theories" are distorted, garbled versions of "what if the US did to white people things that it has done to black people".
