The cops can't be there if a bad guy decides to open fire. They can only be there AFTER the crime is over. No American wants to be arbitrarily stripped of their right of self defense by politicians and bureaucrats - and in any event, no law can foresee all the situations that might happen.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus