The problem is that you can't reliably pre-screen for terrorists, the signal is plainly undetectable in the noise - there are 95 million passengers a year at Atlanta alone and 19 hijackers on 9/11.
You're bound to get a lot of false positives, and then what do you do with them? In the meantime, the actual terrorists just wait until they successfully get a guy pre-screened, and he then just walks on board with a bomb.
The problem is that you can't reliably pre-screen for terrorists, the signal is plainly undetectable in the noise - there are 95 million passengers a year at Atlanta alone and 19 hijackers on 9/11.
You're bound to get a lot of false positives, and then what do you do with them? In the meantime, the actual terrorists just wait until they successfully get a guy pre-screened, and he then just walks on board with a bomb.