What do you not understand about the words "Global War on Terror?"
"Global War on Terror" means more than finding and killing those responsible for 9/11. That's just vengeance and it won't solve the larger problem.
What it does mean is finding and confronting terrorists and terrorism where it incubates and eliminating it as a viable form of political or social change.
That's what terrorism is--it's not Holy War, it's simply an indiscriminately violent way to get a message or a cause broadcast through the world media in order to effect political or social change.
If we leave Iraq now, for any reason, we will vindicate every suicide bomber that has ever flipped his own switch, every airline hijacker , and every car-bomber who has walked calmly away from his impending violence. Every potential Osama Bin Laden and Timothy McVeigh will think, "Terrorism can make my dreams of change come true!"
And likewise, every time you march in an anti-war rally, regardless of your personal intentions, you are playing directly into the hands of the terrorists. What do you suppose one of the Syrian fighters in Iraq thinks when he reads about massive protests in Europe and in the United States? He is encouraged. He thinks that his message is being heard and that his strategy is working (strategy, by the way, which includes using little girls as body armor and crowded streets as battlefields).
In Somalia and in Lebanon we taught the terrorists to believe that if they kill enough American soldiers, we will give up and leave. We now have a chance to re-teach them. Let's change that belief.