Dehavilland Driver, I would guess your summation of the political imperative is probably accurate. As to who is screening the screeners. Who is screening them for intelligence might be more to the point. Or even, is it possible to rely on an inate intelligence of people in such a role.
It would seem that the 11/9 hijackers, rather than get too complicated in their plot used the lowest common denominator, the sceener's lack of intelligence and inbred indifference to the ways of others.
How pilots who for the most part have always been the good guys are now being treated with outright suspicion is perplexing.