To put it another way, if throwing feces was common behavior among humans, you might say "this isn't a human problem, it's a primate problem." And you'd be right, in a sense. But the key point is that throwing feces (as well as violence) is more easily avoided behavior for humans than for chimps. A human might choose to yell to express a level of anger than chimps only express with feces throwing (I might be uninformed about the feces-throwing behaviors of chimps, but you get the point). When we fail to take advantage of opportunities to avoid violence, we should ask ourselves why.

That is, I agree it is not an excuse to say "animals do it." But, it is also somewhat askew to me to have a barrier to our explanations that do not involve "humans are just animals."