There are people who believe that an armed society is a safer society. I call those people douche bags.
Having a firearm in that kind of situation won't necessarily mean that the amateur is going to become a hero. It could just mean that a bunch of other innocent bastards get caught in the line of fire. Look at how many shots are fired by cops in those situations. Ultimately, they empty their magazines, reload, empty them again, and hit the perp once in the ankle. A firefight is an ugly, horrible thing.
Talk to any soldier about his first real fire fight. They'll tell you a story of panic, confusion, and horror. And those are people who trained for that situation religiously.