There was a time when all the men and a few of the women in that theater would have done either a concealed carry or an open carry. Most of them would have been good enough shots to dispatch this shooter, too. - These types of Jokers would know it (they did back then, too) and it would have served as a deterrent. If the next Joker gets shot directly in the gas mask, that’ll stop it for a long while.
I understand the theater specifically asked patrons not to use conceal carry. There were signs advising of this.