Sir? Step over here, please.

If a doctor (or inventor, or company, or whoever) invents a medical device to cure or treat some sort of sickness or disease or disorder, she can't use it, can't put it into practice, until she's proven that it does what she says it does.  Why aren't security professionals held to anywhere near that standard?  

I'm pretty sure stents for atherosclerosis weren't used on a patient in a hospital before somebody asserted to somebody else that those stents did something useful, and backed up that assertion with some kind of proof.  Did any similar process happen before airport security started demanding that we take off our shoes before we could board a plane?