I am dismayed by the large number of participants here who resort to emotional arguments or to attacking the character of another participant or group of professionals. Sure, given the danger that is presented by an actual terrorist (as opposed to a little old lady with an artificial knee, which often prompts TSOs to go ballistic and prove their unlimited powers) there will be disagreement about how best to minimize the risk. That's no reason to be inflammatory.
The point I wish to make is that once a real terrorist gets on board an airliner, everything the TSA has done (or failed to do) is no longer relevant. The question of arming FFDOs boils down to this: In case of real terrorists on board, is it better for a flight crewmember to have a gun and not need it than it would be for a flight crewmember to not have a gun but need one?
Tens or hundreds of thousands of flights have been conducted by armed FFDOs without incident. There have been a whopping two (2) incidents, one of which was not even on a plane. I don't care who has "had more training" or who "knows more about law enforcement". I'm quite comfortable flying behind an FFDO who is armed. If I can't trust them to be responsible with firearms, then I sure as heck cannot trust them with handling the airliner!