This opinion piece notes that it is "easy" to avoid scanners, and that therefore this is an ineffective policy. He suggests that the TSA should stop doing things half-way.
It is the nature of bureaucracy - particularly 60,000-strong government agencies - to do a mediocre job of everything, full of holes. It is in the best interest of the people working for the agency.
As an aside - it may be easy for some people to avoid scanners, but some people are being targeted (more on this in a future post). Nonetheless, I don't want to risk it; the cost is too great since you can't rely on being able to back-out of the deal without threats of fines and imprisonment.