"As an EMT I have responded to at least one call where a woman called 911 believing she was having a heart attack. We responded to the home and entered it and the husband was standing in the kitchen completely unaware that his wife had called for our services. If he’d been armed and under the premise that he would shoot any stranger who was in his home he would have shot the very people responding to his wife’s call for help."Too many people get a gun and then look at it as some sort of universal problem-solving tool instead of a fairly narrow-focus bullet launcher.
Everybody expects it's going to be nazi zombie bikers come to rape their TV and steal their dogs. Nobody expects it's going to be the developmentally disabled adult child of the previous owners of your house coming "home" to make himself a sandwich. Further, there are places where you might be legally justified in shooting someone but, well, "Hey, it's okay, you didn't know he was a 70-y.o. Alzheimer's patient" probably doesn't help the Ambien work any better at 3:30 in the morning...
EDIT: This ties in with stuff talked about here, too.