Fact of the matter is you can't be everywhere all the time. It's just not possible unless the police forces multiply by a factor of 100 and literally post people in every place people are and that is a completely different issue. People need to be allowed to protect themselves because the police are usually not going to be there to stop whatever is happening until after its done.
Police, usually, are a reactionary force and not a preventative as it should be. Locking people up because we think they MIGHT do something burns too many constitutional amendments its not even funny.
Plus you can only do so much when prosecutors won't press charges, or judges reduce sentences to time served etc for repeat offenders. Sure, keep arresting them but what good does it do when they're back on the street committing the same offense later that day?
