Calling the police is like using regular expressions: now you have two problems. You shouldn't expect them to stop crime in progress: if you actually ask a cop she'll tell you that's not their job. Instead, they show up at some random time after the crime is over and do cop things: detain, intimidate, shoot pets, destroy property, confiscate, etc. Why would you invite anyone to your home or neighborhood to do those things? In some cases you have no choice because you're required by law to call the police. Those are the only occasions upon which you should call them.