As we all undergo even more intense screening procedures at airports, in the fond (if questionable) hope that the new procedures will be more effective than the old procedures at making our air travel safer, I thought readers might find the post Do I have the right to refuse this search?, by a retired police officer, of some interest.
As she notes, the process for selecting people for "secondary screening" seems random at best, and the "pat down" she was given when she refused the air-puffer machine was hardly effective.
I am reminded of a recent book on anti-terrorism I read, that pointed out that if an attacker got to the Uzi-toting agents surrounding the principle being guarded, the last line of defense, then the whole system had failed. The attacker should have been identified and taken out far earlier. It seems to me airline security is like that. If a terrorist reaches the TSA screening process, the whole system has already failed.
Of course, to take out terrorist early requires good human intelligence, double agents in place, watchers looking for people "casing" the site, effective passenger profiling, and a number of other quiet, difficult tasks. It's far easier and politically more popular to spend a lot of money for an obvious TSA presence at the airport than to put in place and maintain the far more effective, but far less visible measures that would make such screening the last line of defense, instead of the only line of defense.