I think a reasonable compromise is the metal detectors, and being able to skip the line. Which is what we have now...

There is no SURE FIRE way to guarantee that you'll bring a plane down, even if you wanted to, with the other pilot there, unless he's incapacitated. We all know that in non critical phases of flight, the other guy would have the reaction time to fight you, and in in critical phases, he's (she's) gonna be watching the controls like a hawk, ready to jump in if something doesn't look right. The easiest way to remove that element is to incapacitate the other person, and that's a lot easier to do if you can sneak something on board that they aren't expecting. Therefore, pilots SHOULD be screened... just not naked body scanned or felt up.