There is a lesson to be learned in the tempest against TSA: be careful what you ask for. After the underwear bomber tried to take down a Detroit-bound Christmas flight last year Congress and the citizenry lined up to cheer lead for deploying body scanners everywhere. Nobody paused to think if that was a wise response.

Non-metalic material hidden under clothes has always worried airport screeners. When someone dressed suspiciously there was only one option–an intrusive pat down. The scanner technology offered an option–a less intrusive way to check on the rare occasion when some one was sent to “secondary” screening (the more thorough going over some travelers get after, or instead of, the normal walk through the magnetometer).

When the decision was made to use the body scanners for primary screening that is when the trouble really started. Now instead of using them for suspicious travelers a wide swath of the traveling public must face the foreboding scanning chamber. Many are opting out of being subjected to the scanners for various reasons. That is their right. But then they have to subject themselves to a pat down and the pat downs are intrusive. So the irony here is that a technology that was developed to require less pat downs is driving up the number.

Frankly, the threat does not justify the indiscriminate use of body scanners for primary screening. Eliminating the threat of serious liquid bombs by restricting carry-on liquids took that immediate danger of the table. Small bombs strapped to bodies or air mailed are far from guaranteed to bring down a plane. Sure any bomb on a plane might do some damage–but let’s face it you could also just stab people in the neck with sharpened pencils to kill a couple of passengers on a plane. And if you wanted to kill a handful of people with a bomb, you could just blow yourself up at the ticket counter before you got near security.

That is not to say that sensible primary screening, or more thorough and rare secondary screening, should end. But we should be spending our security buck where it gives us the biggest bang.

The best security is intelligence and law enforcement that finds and stops the bad people before they get near the plane. Let’s continue to do common sense screening at the airport, but lets stop pretending that is the best line of defense.

TSA should back off requiring the body scanners for primary screening.