Crossing out 'Black lives matter' and writing 'All lives matter' is, to me, the equivalent of denigrating the NAACP because all people deserve advancement. Yes, 'All lives matter' is a true statement. But by writing that you come off as being completely oblivious to context and why 'Black lives matter' was written in the first place.

EDIT: Perhaps BLM could have averted all of this hubbub regarding the phrase if they had just included the implied 'too'. As in, 'Black lives matter too.'