Or what if someone robbed the store, with no intention of shooting anyone until rambo pulled his gun, got into a shootout with the robber and five kids were killed in the crossfire?
Regardless that is a pretty long, BS, what-if case. 99.9999% of the time when you go to the mall nothing will happen. On the extremely remote chance that something does, I don't really believe that the "good guy with gun" fantasy would play out the way everyone thinks it will, except maybe in a true mass shooting. Also why would a guy running from the cops, run into a store with only one way out, then shoot everyone? Seems like a good way of getting caught. Please find me all the stories of five year-old birthday parties being shot up in the suburbs (where open carry people actually live).
If some dude had grabbed a sniper rifle in Vegas, first he probably would've been shot by some other "good guy with a gun." Second, what happens if he missed and now he is shooting into innocent people's rooms? Or do you think it would've been okay for all the "good guys with guns" to start shooting at a hotel with 3,300 rooms hoping to get the one guy?
Sorry, I forgot, a good guy with a gun will never miss and no one will ever mistake him as a bad guy with a gun.