Having recently had to scare someone off about a week ago who tried to break into my house in the middle of the night, I can say that's it's hard to think in these situations. You don't have time to address the situation. You are probably nervous and shaking. You may be disoriented or tired as well.
I heard a sound at 2AM, I went downstairs to see what it was. Someone was trying to take apart the window and get in. I didn't see him very well because he ran off when I shouted at him. Honestly, I haven't slept well since. I'm still jumpy if I hear any sounds, and I was already jumpy to being with. I hate hearing sounds at night.
I don't have a gun. I'm not sure if I want one either. I like to keep a knife or some kind of tool for defense handy, though I have never picked one up because I heard something.
I don't know what I would have done in this situation. Not being much of a gun person has an effect on that, but rest assured that if I got into a fight, I would fight hard. I've never been in a fight because I'm not someone people mess with. I'm in good shape and frequently get comments about looking "big" or "buff" or whatnot, so I've never had to worry about anyone messing with me. I have an extremely short temper though. I frequently smash things. Hell, I've broken my fair share of computer mice and game controllers. If someone made me mad enough, I would probably do about anything.
The problem with these types of situations is that you do not get to be your normal, rational self. Sitting here in safety and saying what you would do in a dangerous or scary situation is just not how it goes.
I don't think the guy should be at fault for anything. If you don't want to get shot, don't break into people's houses. Not everything goes how we want. We can't get a redo. If people put you in a situation like this where you are in fear for your life, you should not be responsible for your actions in this state. It can take a few minutes to return to a normal state of mind, and you may feel shaky or disoriented for the next few hours even.