Many lives don’t much matter to powerful white Americans. Black lives: expendable. Native American lives: valueless. Latinx lives: dismissed. Immigrants, refugees, dark-skinned children at the border: despised and abused. Poor white folks: exploited. All of the above: murdered.
So OF COURSE IT IS NECESSARY TO SAY “Black (and all oppressed or despised) lives matter.” Before God, AND before formal American values, and in our prized religious texts, they matter.
But they must matter in our actual practice. Sadly, IN BROAD AMERICAN PRACTICE THEY DO NOT MATTER. So we need to keep pointing it out, and change that.