The U.S. homicide rate has fallen by over half since 1980, and the gun homicide rate has fallen along with it. Today, Americans are safer from violent crime, including gun homicide, than they have been at any time since the mid-1960s.
Mass shootings, defined as four or more fatalities, fluctuate from year to year, but over the past 30 years there has been no long-term increase or decrease. But "random" mass shootings, such as the horrific crimes last Friday in Newtown, Conn., have increased.
Loren Coleman's 2004 book "The Copycat Effect: How the Media and Popular Culture Trigger the Mayhem in Tomorrow's Headlines" shows that the copycat effect is as old as the media itself. Johann Wolfgang von Goethe's 1774 classic "The Sorrows of Young Werther" triggered a spate of copycat suicides all over Europe. But today the velocity and pervasiveness of the media make the problem much worse.
A second explanation is the deinstitutionalization of the violently mentally ill. A 2000 New York Times study of 100 rampage murderers found that 47 were mentally ill. In the Journal of the American Academy of Psychiatry Law (2008), Jason C. Matejkowski and his co-authors reported that 16% of state prisoners who had perpetrated murders were mentally ill.
In the mid-1960s, many of the killings would have been prevented because the severely mentally ill would have been confined and cared for in a state institution. But today, while government at most every level has bloated over the past half-century, mental-health treatment has been decimated. According to a study released in July by the Treatment Advocacy Center, the number of state hospital beds in America per capita has plummeted to 1850 levels, or 14.1 beds per 100,000 people.
Moreover, a 2011 paper by Steven P. Segal at the University of California, Berkeley, "Civil Commitment Law, Mental Health Services, and U.S. Homicide Rates," found that a third of the state-to-state variation in homicide rates was attributable to the strength or weakness of involuntary civil-commitment laws.
Finally, it must be acknowledged that many of these attacks today unfortunately take place in pretend "gun-free zones," such as schools, movie theaters and shopping malls. According to Ron Borsch's study for the Force Science Research Center at Minnesota State University-Mankato, active shooters are different from the gangsters and other street toughs whom a police officer might engage in a gunfight. They are predominantly weaklings and cowards who crumble easily as soon as an armed person shows up.
The problem is that by the time the police arrive, lots of people are already dead. So when armed citizens are on the scene, many lives are saved. The media rarely mention the mass murders that were thwarted by armed citizens at the Shoney's Restaurant in Anniston, Ala. (1991), the high school in Pearl, Miss. (1997), the middle-school dance in Edinboro, Penn. (1998), and the New Life Church in Colorado Springs, Colo. (2007), among others.
At the Clackamas Mall in Oregon last week, an active shooter murdered two people and then saw that a shopper, who had a handgun carry permit, had drawn a gun and was aiming at him. The murderer's next shot was to kill himself.
Real gun-free zones are a wonderful idea, but they are only real if they are created by metal detectors backed up by armed guards. Pretend gun-free zones, where law-abiding adults (who pass a fingerprint-based background check and a safety training class) are still disarmed, are magnets for evildoers who know they will be able to murder at will with little threat of being fired upon.
People who are serious about preventing the next Newtown should embrace much greater funding for mental health, strong laws for civil commitment of the violently mentally ill—and stop kidding themselves that pretend gun-free zones will stop killers.
Mr. Kopel is research director of the Independence Institute and co-author of the law school textbook, "Firearms Law and the Second Amendment" (Aspen, 2012).