That is true and an important truth at that. But it does not justify the slaughter, rape, or terrorizing of civilians. Some may accidently be killed, some may be intentionally killed when they take up arms, and all will be "terrorized" in general by the war, of course, but intentional targeting and harrassment of civilians is always ignoble. Modern American forces are famous for their restraint in this regard, and I'm glad they are.