I work as an RN on a locked psychiatric unit in a city hospital. Many of my patients are dangerous, violent, drug addicts, schizophrenics, and antisocials. Some of them are ex-cons who did many years for murder and rape convictions. They are out there. They're not always in bad neighborhoods, and they are not always the disenfranchised, misunderstood, down-on-their-luck characters that the media makes them out to be. On a good day they will take your stuff. On a bad day they will take your stuff and beat you, and rape you, and stab you and they'll laugh while they're doing it. You won't realize the danger you are in until one of these guys is in your face and there is no-one else around. It just makes sense to have the means to defend oneself, and when dealing with these characters, the more effective - the better.