Pro-gun folks: No, you would have not have stopped the Aurora massacre. You would have hugged the floor sobbing, or maybe maybe taken some shots in the crowded, gas-filled movie theater with gunshots ringing out and the movie still playing, missed the shooter by about 75 feet, and hit some random bystander.
Anti-gun folks: Dude would have gotten himself an assault rifle whether it was legal or not. I'm with you, but your argument is not here.
My work here is done.