This guy, who seem to known what he's talking about most of the time, got quoted by CNN about post 9/11 airport security.
As he puts it, the mentality seems to be "cover your ass". Nobody in a position to do anything is willing to say "no" for fear that something will happen and they won't be able to say they did everything they could.
This sort of reminds me (by contrast) of the time I was talking to a Philosophy masters student and after a bit of back and forth I asked him the question "Would you rather have security measures that make you feel safe, that you know are utterly useless or ones that don't make you feel safe and actually make you safer?" To my utter shock, he asked for the first.