I know I have expressed my views on this subject before, but I will offer them again.
I was told by an attorney a few years ago that in the event that I had to discharge my firearm, I could expect to pay $10,000 minimum. If the individual died and the prosecutor took it to trial, I could expect to pay $100,000. As a result I tend to measure my response to these scenarios by this measure: If the individual whose life is in question told me they had an operable brain tumor but it would require $100,000, would I liquidate my assets to help them? This tends to reduce the number for whom I would intercede. The exception would be if the individual in question was one who Ryder referred to as "the true defenseless."
Before anyone decries the fact that I have boiled it down to strictly finances, let me add a few other comments.
First, I am not a law enforcement officer. In any situation where I have a firearm available (at least in the United States) I had to obtain a permit just as any law abiding citizen could have. The simple fact is that the individual in jeopardy could have/should have obtained a means to defend themselves and did not.
Second, a frequent arguement made in these discussions is that becasue I have the means I bear an obligation to my fellow man. I think that the arguement that having the means available to help ones fellow man obligates one to provide assistance is nice in theory but is put in to practice much less frequently than we would like to admit. Suppose you were driving with your wife and two small children on an interstate late at night and saw a couple of rough-looking individuals with their car broke down by the side of the road. Would you stop and offer them a ride? Why not, you have the means. If your answer would be to call the police and let "the system" provide the assistance, why then is this not an acceptable answer to the scenario proposed by Clipse? Ditto for doing nothing.
I think there is a somewhat romantic notion that Hollywood implants in our brains about how wonderful it would be to be the "good guy" who guns down the "bad guy." But real life is not Hollywood and there are consequences to this type of action, justified or not. A dead spouse, a prison sentence or financial ruin are three big ones in the scenario mentioned.
As unpalatable as I may find it, I will content myself with the knowledge that if trouble finds me it will get much more than it expected.