There are approximately 150,000 federally-attached law enforcement personnel. Another 750,000, roughly, state and local cops are employed by our various government arms. Of those various officers well more than half sit behind a desk and haven't left one gram of shoe leather on a street or in a cruiser in the last year. The majority of you fire your weapons for periodic qualification and they have never been warm or dirty besides. You've never faced death, you've never had a weapon pointed at you in anger, and you've never drawn your service weapon in the line of duty. Those are facts.
Now consider the "bad side" of America. The Justice Department estimates there are at least one million gang members - active gang members - in America. These people, mostly young males, have nearly all drawn or fired weapons in anger. They are responsible for more than three quarters of all crime in this country, and some eight out of ten violent crimes. Those gang members have families - younger males who are "coming up", "friends" (if you can call a murderous thug a friend) and others. Between all of those "loosely attached" folks and the hard-core inner circle itself we probably have somewhere between 5 and 10 million people in this nation who, given the wrong sort of provocation, might decide that "Zombieland" wasn't just a movie.