Remember the post on the Israeli student who killed the man who was going around shooting people on a university campus? He killed him because he had a gun and used it to put an end to something that could have been much, much worse had he not have been armed and on campus.
In regards to that post, Misawa over at Misawa's Musings has fleshed this issue out a bit. I would encourage you to stop by over there and take a look at this thoughts on the matter and offer your own. While you are there, read some of his other posts; he has a knack for putting things.
You can read more here.
Comment on his blog on this one.