The folks who believe that only the police & military should have firearms make the point FOR us: the only thing that stops a bad guy with a gun is a good guy with a gun.
They simply limit the definition of "good guy" to police and military. History shows, time and again over the millennia and as recently as the past decade, that the greatest number of civilian deaths in the world are at the hands of the peoples' OWN government. Always preceded by disarmament "for greater safety". Always.
As a side story, the police are notoriously bad shooters. After watching the Cambridge MA cops use our (MIT's) range for practice one day, I used to tell people that if the Cambridge cops started shooting, go stand right in front of them as it was the ONLY safe place. Just watching them scared the dickens out of me and I was astounded that no one got hurt. My coach, who was retired from the Providence RI police force, had hours of hysterically funny, terrifying, stories about the Providence PD folks.