You sure ask a lot of questions!!!

As far as any of these above

1. None
2. Have you been through an airport? It's a joke really, but they get lucky once in awhile. Audit's of the TSA screenings have shown they miss more than they catch.
3. Partial illusion, partial practicality. There's always a chance plots etc.. will be discovered. Personally, I think these acts' should be discovered before the culprets ever make it to the airport. This is a last line of defense!!!(And personally, I love the idea of the FFDO program[pilots w/ guns], I'm eventually going to get my conceal and carry for personal reasons, but it's a right that I feel everyone should exercise or at least respect)