Do people even realize how bad it is for the US to lose its credibility?

Not every war is a war of annihilation, especially not in Iraq when we don't want to annihilate the country. The vast majority of American wars have ended with negotiations and diplomacy. To lose our credibility is to take another weapon out of our arsenal. Do we want allies or not? Do we want the Iraqis to trust us and cooperate with us or not? Doing a sneaky little thing like that would make us look like a bunch of liars, which they probably think we are already, and won't accomplish much even if we had succeeded. Do you think all the Shiite militias will just pack up and embrace American democracy if he had died? Do you really think no one else would step up to take his place? Studies reports that a pure military victory is impossible in Iraq but through a combination of military and political means we can still win. If we can pacify Iraq we would have won.

Stop painting everyone with a single brush. Al-Sadr is the leader of Shiite insurgents, not a terrorist. Sunni insurgents cooperate with al Qaida but fight the Shiites. Do most of the communities even know this? Yes he leads a group of people who have killed American soldiers. Guess what, so did the British, Germans, and Japanese. With the exception of one war, we ended all those wars with those countries through diplomacy and treaties. This is a war. Did you really expect the Iraqis to throw up their arms and not fight us when we're occupying their country? The best we can hope for is for them to trust us and convince them of our good intentions.