Because no American was forced to commit war crimes in Iraq. Yes, participating in an attack on a state that is of no imminent threat to your own is a war crime. Brainwashing may have been an extenuating circumstance, but a lot of Americans were staunchly against the war so how come they let themselves be brainwashed? If I join a gang can I claim to have been brainwashed when most people in fact do not join gangs? People are responsible for their own actions.