On my aircraft we are already armed... but not with guns.
I reckon I could do more damage with my nice sharp crash axe with x mg of adrenaline floating through my veins as I could with a little handgun.
And there would certainly be time to be ready for it as they kicked the secured cockpit door off its hinges.
But lets be realistic. None of us would stand much of a chance, guns or no guns, if we were up against a team of vaguely organised terrorists even with minimal weaponry.
I agree totally with previous posts as to stopping these guys getting on in the first place. Intelligence and security at the terminal is where its at, boys and girls. THAT is the last line of defence, as far as I'm concerned. Everything we do on board is playing succour to the media frenzy. Faced with a situation, I don't think guns would help one iota.