Writing at Vox, Dara Lind tries to explain why saying "all lives matter" is deeply offensive to black activists. They shouted down Democrat presidential aspirant Martin O'Malley when he said it. He later apologized.
The truly odd thing is what black activists mean when they say, "black lives matter." They actually mean the few "black lives taken by whites matter." Or even, "black lives taken by white cops matter."
Little interest is shown in the overwhelming majority of blacks murdered by other blacks. Shouldn't they matter too? Apparently, they don't.