[aSkeptic]

Why wait around for something to happen? Some of us would rather "stop the invaders" in their own countries before they attempt to deliver WMD to our friends and loved ones.
1. Searching for suspects on a foreign turf is harder than watching out for people illegally crossing the boarder (who are suspect by default). If the teleporter was a reality, I think I'd opine with you.
2. 9/11 and acts of similar intention were performed with common consumer objects. Is a passenger jet or fertilizer a WMD? Obviously it depends on who, why, what, where, AND when.
3. Throwing out all foreigners on expired visas is doing something.
4. Current maintenance on 2 countries, and a war on 5 or more other countries will spread our military resources thinly. That could make us vulnerable to opportunistic superpowers to be.
5. War is damn serious business. We are the best at doing it with the fewest casualties but it doesn't change how disruptive it is. I wish to conserve the good image of the USA.

[mac_truck]

1) Difficult but not impossible. No one said asymetric warfare was "easy".

2) 9/11 proves that waiting for the bad guys to show up at your door step doesn't work by itself.

3) How many of the 19 were here legally? Waiting for visas to expire is not doing something.

4) The price of freedom is eternal vigilance. We're just getting started. Our enemies better get used to it.

5) War is disruptive? If you are referring to those who threaten our existance, lets hope so.

My advise to you is "take the blue pill..."