We're fighting against a people that have no problem strapping bombs to their children and sending them off to die.
They need to be beaten decisively. Terror is what they understand. If you're trying to teach someone a lesson, you need to put it to them in a way they'll understand it. Anything less is a waste of time, effort, and in this case American lives.
We need to commit a 9/11-style attack on Afghanistan to make them understand.