Dr Dave,
You are starting to come up with some rather obscure what/if scenarios. How many pilots have you heard of that have assisted or committed acts of terrorism ? I can think of just one - the Russian Captain some years ago that committed suicide by crashing his aircraft with passengers on board. He didn't need a device to do so.
Have you thought about the shops selling liquids once you have passed security may have been infiltrated by terrorists ? You can come up with no end of potential scenarios.
Aviation, train travel, driving a car etc will never be totally fool-proof. All we are asking for is a little common sense.
Regards
Orion Man