OK, but don't go into over-simplification mode.
9 out of every 10 people in that theater might be armed, but all they see is one person with a gun chasing another person with a gun. Or more likely, they see one person chasing another, and unless they are right up close they don't see whether there are guns. What can all those people do to prevent the good guy from getting hurt by the bad guy, and how do they even figure out which is which? You all say, we are responsible and will do nothing until we know the facts. So how does that protect anybody? You WON'T know the facts until it is too late. Or you say, we will only use the gun to protect ourselves. OK, very good, nobody was under threat in the theater except the girlfriend, but of course you don't know that, so still you will do nothing until it is too late for her. The only reason the cop got involved here is because she IS a cop and her mind-set is to intervene. That's exactly opposite the mindset each of you is expressing, that you will stay out of it unless you yourself are directly threatened.
I grant you, in certain unique situations you may be able to protect yourself and your loved ones if you are armed. But YOU have to "go into OMG extrapolation mode" to specify those situations. Don't pretend that there many OTHER situations where your packing heat will help ANYBODY.
I wasn't going to answer because your stance is obvious. But here goes.
You make a bunch of assumptions about the abilities of cops. This isn't tv here. We say we would not do anything until we were sure. That is a bad thing? Neither will a cop, but if a cop shoots a good guy, to bad. If I shoot a bystander or good guy, holy *censored*! I am untrained and reckless and irresponsible! Of course I would stay out of it. I don't know what is going on and I carry for MY protection, the public at large MAY get the benefit and maybe not. See what Smitty said.
You cannot possibly cover all the situations that could arise and neither can the cops. You have to use your best weapon, your brain. I realize some are handicapped that way.
Bottom line, your just inventing scenario's and telling us we don't have what it takes to handle any situation. You don't know that and it happens all the time.