All lives SHOULD matter. The “Black Lives Matter“ movement was born out of a cry for recognition of the demonstrable evidence that black lives matter less than white lives to the criminal justice system.
The statement isn't that black lives matter more, but a reminder for society and the criminal justice system to include the black lives in the "all". Once equity and justice is established within our systems, we can then join you in chanting all lives matter - because then, they would.
For now, when you attempt to stifle a movement for justice by making it seem as though it is pointless, or deny the discrimination and systemic racism that exists, you are part of the problem.