Well, i thought about this, and then had to consult our greatest source of modern wisdom...
...We all saw what happened to Peter Parker when he decided "Hey this isn't my problem." and stepped off to the side. Because of his decision Uncle Ben got a cap busted into him and now Aunt May sleeps alone at night...
Seriously though, we had a little girl (Esme Kinney) murdered here not too long ago. Anyway, the guy who did it had a rap sheet a mile long, and had served time before for manslaughter and arson. There were many opportunities where if citizens had been armed while he attacked them perhaps he wouldn't have had a chance to be acquited of so many other charges (propositioning a minor, rape, buglary) that would have put him back in prison where he belonged.
So, for those of you who retreat when you're able to do so. What happens if the person you could have stopped goes on to kill a 13 year old girl jogging around a park? Doesn't a moral obligation exist to remove dangerous elements from society if the situation is presented to us?
And please, let me be clear, I'm not going out and looking for trouble. And I pray each and every day that I NEVER fire a shot in anger. I just would hate to not do something that allows a criminal to go on to commit horrible crimes...
It's an interesting question either way.