Rambo, Captain America, G.I. Joe, and Ben Carson

Ben Carson (like Monday-Morning Quarterbacks all over the country) knows exactly what he would do if confronted with an armed gunman:

"I would not just stand there and let him shoot me. I would say 'Hey, guys, everybody attack him! He may shoot me but he can't get us all!'" (source)

I once witnessed a violent crime from just a few feet away.  It was near Christmas, the mall was packed, and a man came up behind the woman next to me.  He hit her in the back of the head with one hand, pushing her chin into her chest, and with the other he grabbed her necklace and yanked backwards.  The chain snapped, and he took off running through the crowd while she clutched at her neck.

By the time any of us realized what was happening, he was gone.  There were probably dozens of us who could have stopped him, but those few seconds gave him an edge we couldn't overcome.

A semi-automatic handgun fires as fast as you can pull the trigger.  How many times can you squeeze and relax your hand in three seconds?

(And, for what it's worth, Chris Mintz did confront the gunman.  He was shot seven times, and it didn't change the outcome one iota.)