Avgas,

The point is deterrence. Just having armed pilots on board greatly reduces the odds of a hijacker being successful. The smart ones will choose easier targets. (And don't tell me the guys who pulled this off weren't smart.)

If a situation gets to where bad guys are killing off cabin crew and pax, where would you rather be: in a place where the good guys can fight back with superior force (or at least more equal force) or in a place where the good guys are defenseless. I know my choice.