Hi all
The issue is not truly about who is more trustworthy: it should instead be in minimising the requirement for placing sole trust in any one individual.
A single individual with a hand gun can 'control' an aeroplane more easily than any one individual without. This is a big problem with the sky-marshal concept as well. The first sky-marshal to get bent or escape background checks will kill the other onboard, then have free access to the crew. Even with better cockpit door procedures a sky-marshal on the lose would have a better idea of how to bluff or con his/er way through it than an outsider.
Face it, repetition of Sept. 11's exact method has been impossible even by the finish of that day, and quite possibly by the finish of the fourth crash. Without much better cockpit doors, an armed pilot caught by surprise just makes it possible again: not at all the desired option. A second problem is that it makes the single pilot suiciding the plane that much easier. A third person on a secured flight deck would be a safer 'change', IMO.
Off to do some work now.