I'm pretty certain that most pro-gun nutcakes have never used a gun. It's pretty hard to nail a moving object, especially with a handgun. I use guns, know how difficult it is, and laugh at what some of you have written. Compound this by a dark movie theater, your own panic, and the panic of others. It's not like in the movies where all ya do is calmly whip the thing out and aim and you mow down 100 bad guys in 2 seconds like Bourne or Tom Cruise or Avengers.
If there had been just 10 people packing handguns in those movie theaters, I can almost guarantee the body count would be far greater. People would have been bumping into you, your hand would be shaking, you'd be moving, the target would be moving, people would be getting into your line of sight, pieces of the human beings and the theater would be blowing onto your face.
On top of that, the guy had body armor. So your shots (had they even connected, probably wouldn't have hurt him). And by the time you would have hurt him, 10 other people would have been wounded by your shooting.
A movie theater is a horrible place for a gunfight. There are only two stairways and a ton of people to get in your line of sight. Had you charged the shooter, he would have quickly mowed you down (his guns were pretty damn lethal.). Had you jumped to one of the sides, you probably would have broken you leg and taken you out of the game right there. You couldn't sit behind a seat and have a shootout with the guy since it was a packed house and people were running to get away.
Literally, the only option would have been to lay as close to the ground as possible and try and ride it out.