Sigh, the crazy train keeps rolling. Sure, let's not blame the victims or anything. No offense, former Sen. Russell Pearce, but shut the fuck up.
Look, I have some training in firearms (and I have all the training required to hold a concealed carry permit in the State of Ohio). I'm actually a pretty damn good shot. But in a darkened theater with flickering lights, the chaos of the crowd, the smoke from his grenades, and the adrenaline that would be pumping through me at that moment, I wouldn't even try to take the shot because it's a damn good chance (I would put it at over 99%) that if I would hit something other than a wall it would be another audience member.
Plus, and I can't stress this strongly enough, the fucker had body armor on. The only shot I would have tried (and that anybody would have had a chance of making) would be center mass. Dear Senator, guess where the fucking armor is (police reports also say he had a helmet, leg protectors, and throat, neck and face protectors). The only way to have dropped him would have been a head shot, or arm or leg shot (see comment about extra protection, probably wouldn't have been successful anyway). Damn difficult shots to take quickly in the best of circumstances, impossible in those.
And I hate to tell you this, but your hero worship is woefully misplaced and the result of brain washing from watching too many John Ford type westerns while grown up. You've been telling yourself lies about what people actually do. It takes a lot to rush a cabin that has someone with a knife inside. It takes a hell of a lot more to rush an active shooter.