That's a good point,
I guess part of the solution is the US policy in the middle east. I know it's easier said then done but that's where the problem needs to tackled. I am always amazed to see so many countries protest US involvement in the Middle East but now that the proverbial !!!!! has hit the fan they are all begging for America to get involved... at least that's what they are saying on CNN.
Personally I think it's about time America got uninvolved in the Israeli/Palestinian conflict but they say that our involvement helps our strategic interests RE: IRAQ by keeping our allies happy (Turkey, Jordan etc..) ANyway I get off the topic.
You are right, there is no fool proof method of security, there always has to be a compromise between practicality. That young 15 yr old may well have been carrying a photo ID when he flew his plane into the Bank of America building.