Some one you love has gone off his rocker and is about to through a hand grenade into a crowded street. The only way to stop him is to shoot and kill him. How you got a gun and you're buddy got a grenade is irrelevant. Do you kill you're loved one, or let him kill a dozen or so perfect strangers?
I think I agree with D. I think I SHOULD shoot my beloved friend, but... will I? I'm not sure. Maybe I could just shoot them in the hand or knee, thereby knocking the weapon out of their hand and incapacitating them so they couldn't lob the grenade at all. But, if they already pulled the pin, this will cause them to be blown to bits anyway.
More than likely, I would freeze up. It's like being a passenger in a car and you see an obstruction on the road; sometimes, all you can do is make strange noises as you attempt to warn the driver. I just don't think I COULD shoot them! The time it took to work the nerve up and settle the ethical question in my mind may be too long.
Should my buddy be stopped? Absolutely.
Could I shoot him? I don't know. It's something that cannot be ascertained until the event happens, but I'd like to think that I would try.
Would I shoot to kill? I'm not a good enough shot to go for a fancy targeted shot at the hand or arm or grenade. Center of mass is what I would need to aim at. If I am lucky, he'll just be wounded. Id I am really lucky, I'll find some other way to stop him without having to shoot him.
of course you let him throw the grenade - then a dozen people all get to go to heaven without having to wait around another 50 years or so. then you ask your buddy to repent before shooting him so he goes to heaven, too.