Imagine if 1 person in that colorado theater had a hidden firearm with decent aim? He could have probably moved close enough in range as mr crazy was firing on others and taken him out, or at least stun him enough to jump him.
They would have died. This isn't a movie, or Call of Duty. The shooter was wearing full body armor, and a helmet. In a dark theater. With smoke bombs going off. With people running and screaming.
Nice fantasy, though.