If it were as easy as the TSA-Detractors said it was, it would have been done. It's not that Islamists are stupid (though many are), nor that they are ignorant (though many are). It's not that they aren't willing to try, try, try again - just not the 150:1 kill ratio in Iraq or the 100:1 kill ratio in Afganistan.
The answer is easy: it's not easy to build a time bomb, it's not easy to get one on an airplane, and it's not easy to plot without betrayal.
Duh.
Look, if middle-aged middle-class corprate warriors ever decide to get all terrorist on the world, it'll be ugly - we know how to get things done in a complex system where betrayal is the norm. But we won't - we're all basically conservative, whether we vote D or R.