As I said before, a lot of people get their ideas about guns, crime, violence and what it means to "defend themselves" from movies. The good guy is a great shot, never hesitates, always knows exactly where and how many bad guys there are, and of course, the music changes when the bad guys show up so everyone knows exactly who they are. Movie death is clean-- no brains and guts splatter on the good guy. And the good guy is totally cool about shooting people. He never freaks out, passes out or vomits. He never makes a mistake and shoots the wrong person. And if the good guy does get shot, it is in the shoulder or arm, never the brain or spine so he is disabled for the rest of his life.
In real life, none of that is the case. You are coming home from work after dark and a man approaches you and demands your wallet. Where is your gun? If it is not loaded and in your hand already, you have zero chance of "defending yourself" with it. If you reach for your wallet and come out with a gun instead, you have just increased your chance of getting killed as well as robbed, because you don't know if he has a friend hidden nearby waiting.
You are leaving the ATM with your cash and a group of thugs surrounds you and demands your money. Same question: where is your gun? If you can get it out, how many of them can you shoot before they take your weapon away and kill or disable you with it? You would have to shoot first--before the people get close to you, and ask questions--like, were they really going to demand money, later.
As a woman, maybe I should carry a gun to protect myself from rapists. I would need to have my gun in my hand, ready to fire at a moment's notice, because by the time a man has grabbed me, it's too late. Any man who makes me nervous is fair game. Right?
As for the possibility of "taking out" a crazy gunman in a public place, like a movie theater, school, mall, or Naval base (!) again the reality is very different from the movies. Nobody really knows what is going on. People are running around and screaming. Broken glass is flying around, maybe there are wounded people bleeding in front of you. There is a lot of noise and a lot of smoke, maybe it is dark so you can't see clearly or hear exactly where the shots are coming from.
In all the confusion, you see a guy running by with a gun in his hand. Do you shoot at him? Maybe it's the shooter, or it could be an undercover cop or plainclothes security person, or even another private citizen trying to be a hero just like you. Bullets ricochet and go everywhere. Chances are good that more shooters will create even more chaos and death.
My grandfather, a mean, tough old bird, kept a loaded shotgun behind the front door of his home. I am not advocating this, because he was crazy paranoid, but I want to point out that he had only one gun. He never to my knowledge used it for anything other than hunting, and he did not feel the need to have lots of weapons to feel safe. I have another relative who is an NRA member. He collects guns. I don't know how many he has, but he never feels safe enough.
How does having more guns (say, more than 10 handguns and rifles) increase a person's ability to defend themselves against crime? Are you going to walk around 24-7 with all those guns? Are you going to have them loaded and hidden in various easily reached locations throughout your home? Does this seem like a safe thing to do?
The way for us to be safer is to make our society safer. There are many countries where people don't own guns and crime rates are very low. What they do have: well trained and well paid police, health care for everyone, expanded social services-- especially for the military, drug counseling, mental health care, good schools, jail for violent criminals and alternative programs for non-violent crime.
In the US we seem to have decided to let everyone arm to the teeth and hope for the best.