War does not change the human heart. It ends specific threats from particular aggressive forces. It does not put an end to the fundamental evils that beset mankind. It can put an end to Hitler, Tojo, and Mullah Omar.
It can also destroy the power base of evil ideologies. There are to be sure Neo-Nazis in the world, because there are still stupid, evil people in the world. War can't change that. But Nazism no longer has a state and the resources of a state under its control with which to pursue Nazi ends. The reason this is so is that the Allies smashed the Nazi state in Germany into little bits. By war.
To suppose that any fundamental human evil can be fixed by state action is to be a utopian boob. But we can fix Saddam, and that will be enough to be getting on with.