Also, I know blowing up or taking over an aeroplane has far more impact that attacking anything on the ground, but surely long queues of densely packed adults and children waiting to get through security are an excellent target for a bomb?
You could wheel a suitcaseworth of explosives in and nobody would bat an eyelid.
I guess my point is: we should carefully scrutinize every civil liberty that is taken away from us. In fact, I hardly consider a bottle of water to be a "liberty", it implies you somehow have to earn the right to have it.