Massey AvMan,
You ask where to draw the line, why not ask yourself who can bring down an airliner without smuggling anything through airport security and you will have a good answer.
One thing you have missed is the fact that most of us pilots are not asking to be totally excluded from screening, we just want it to be sensible i.e. screen us for guns and bombs, not nailclippers and water.
How do you suppose a caterer can bring down an airliner without smuggling anything through security?