The hijackers and plotters want us to retaliate. Otherwise, they would not have attacked us. They hope we retaliate in a way that will unite the Muslim world against us, and so we must avoid that at all costs. We must and will retaliate...
Exactly. Our over-reaction is what they hope for more than anything.
...but we must do it in a way that retaliates only against the people directly supporting and harboring Osama bin Laden.
We need to broaden our view a little -- it is quite possible that Osama bin Ladin was little more than a minor player in this. Anyone who aided, abetted or supported these acts is a legitimate and necessary target, irrespective of whether connected to bin Laden.
Exactly. Our over-reaction is what they hope for more than anything.
I disagree. Terrorists don't always (or even usually) seem to have an end-game, unless you count creating chaos as an end-game. They are simply trying to disrupt, demoralize, fracture, and spread terror (thus the name). I don't think the group who did this has a great strategy planned out beyond this. They have already succeeded beyond their wildest dreams by bringing down the WTC and hitting the Pentagon.