NY Madman had the best answer, one I've been saying to anyone who will listen since about September 12, 2001 . . .

The airlines need better doors to the cockpit. Guns don't matter a damn if the terrorists can't get on the flightdeck.

If the terrorists are armed, can they kill some passengers? Yes.
Can they kill all the passengers? Yes.
Can they depressurize the plane? Yes.

Can they take control and fly the fucking thing into a high-rise office building or miltary complex, killing thousands and throwing the country into a full-on pant-shitting frenzy? Fuck no . . .

What did the 9/11 guys have? Box cutters?
Maybe if the doors weren't cardboard, it wouldn't have happened . . .