Liberals are crazy if you think someone couldn't shoot a gunman in a theater because its dark. You can see people. If some fool was standing over you with a gun you could see well enough to shoot him.
Would armed citizens sometimes lead to crossfire casulaties? probably. Would armed citizens stop mass killings? probably not because reaction time will always lag behind someone with a plan. It could though stop some earlier. But everyone being armed would be pretty scary. Sure it makes you safer but only if the other guy is unarmed.
I haven't made my mind up yet on whether open carry would make people safer. I tend to think it wouldn't. Still though i do believe if i was armed and in a theater while someone was shooting people I would have a reasonable chance to shoot him with my gun.
Might have to wait for your shot but you could get one.