Many anti-(Iraq)-war folks are actually truly anti-war (pacificsts). They believe war (and the killing/responsibility associated with it) is inherently bad and must be avoided at all costs. These folks are the mirror image of the classical warrior who believes that war/courage/victory/glory is inherently good. They are both irrationally obsessed with war, both fetishizing kiling and death. They are both, fundamentally warriors, just handling that fetish in different ways.
Both these views are ancient and basically religious. They contrast with the modern (secular humanist view), propounded by Clausewitz, that “war is the continuation of policy/politics by other means.” The purpose of war/politics/policy is to achieve ends we consider desirable. The correct assesment of whether the Iraq/Afghan wars are good/bad for the US is in terms of goals such as strenghtening/weakening the US vis-a-vis likely enemies, increasing/decreasing the risk of WMD terrorism, increasing/decreasing the risk of oil supply shocks (to the economy), impoving/degrading the quality of life for the Iraqi people, etc.
The question is whether you are mature enough to take responsibility for the choices you make. The fetishizing of war is about whether the gods reward/punish killing. The modern view is that people will die/be-killed no matter what choice you make, so you have to take care to choose well.