Because you don't know what to expect from people with certain mental issues. If I see someone pacing outside my office while screaming to the devil and hitting

Because you don't know what to expect from people with certain mental issues. If I see someone pacing outside my office while screaming to the devil and hitting his head, I will try to avoid him. Sure, maybe he will continue to have a mental breakdown without getting me involved, but I don't know. Now, I don't mind calling some authority other than the police, but I would prefer that if the person with the mental breakdown gets violent it will be directed at a professional who knows how to respond