Food for thought

I know it's a grim topic, and it's too soon, but I'm hearing a lot from the pro-gun types about how the Colorado killing thing could have been prevented if everyone had a gun...

...Even if everybody had a gun, how could the Colorado tragedy been averted by everybody having a gun? I mean, if a guy pulls out a gun on a crowded theatre and randomly starts shooting people, I'm imagining:
1. Most people are sitting in their seats, fully immersed in the movie and stuffing handfuls of popcorn into their mouths. If someone starts shooting, much less repeatedly shooting with a semi-automatic rifle, how many people will be killed or hurt before everyone else pulls out their own gun and starts shooting the suspect?
2. I really doubt that people in a dark theatre will be able to aim very well in the dark. How many other people in the theatre would be killed by stray bullets? And even if you kill the original suspect, with everybody shooting everybody else, how can anybody know that the original suspect had been shot so they can put down their own weapon?