> Why is this considered good / normal / expected, but s/men/blacks/g and s/women/whites/g
...because the former holds true across correlations (and is difficult to confound anyway, since the group 'men' and the group 'women' are distributed in like proportion through correlated groups - rich and poor, white and black, around the world, etc), while the latter is very difficult to convincingly show because controlling for economic status alone eliminates more than half of the gap.
Men are genuinely, testably, provably, empirically more violent than women. It's hard to apply any numerate approach to the data which does not support this conclusion. The correlation between melanation and violence is murky and very plausibly non-existent except as artifacts of confounding factors.
Moreover, the definition of "violent behavior" for the purposes of essentially all major research on this topic excludes major wars. If you include projection of military force around the world, it seems likely that the violence perpetrated by white folks is likely to be proportionally greater.
> Morally, neither is, as we should treat people as individuals, not as members of X group.
I broadly agree with this statement, but I think we can still, eg, teach boys not to rape without running afoul of this standard.