It's a self feeding cycle. When you know other people are walking around with guns, it's much easier to jump to the conclusion that someone smashing your window might have a gun as well and might attempt to use it on you. When you live in a society where guns are fairly rare, and indeed the police don't even carry them, then your fear of being shot is a tad less i'd say, therefore you don't have that thought pop in your head of someone attacking you having a gun... you probably just figure you might get in a good fight.

Guns begat guns etc...