Well, no one attributed volume to it. Actually,
@Frangala posted the official data showing the volume earlier, though. If you're curious.
The fact that that it's such a high percentage of young male deaths on its own is the concern (regardless of volume).
And no one is saying that Blacks are inherently more violent culturally or anything to the effect. But murder is, indeed, the leading cause of death for young Black males.
Other groups are mostly not dying in similar ways, or to the same proportion. Murder is not the leading cause of death for any other group of males. And the percentage of people being murdered is not as high for any other group.