Richard Friedman, M.D. in The New York Times:
In the wake of the terrible shooting at an elementary school in Newtown, Conn., national attention has turned again to the complex links between violence, mental illness and gun control. The gunman, Adam Lanza, 20, has been described as a loner who was intelligent and socially awkward. And while no official diagnosis has been made public, armchair diagnosticians have been quick to assert that keeping guns from getting into the hands of people with mental illness would help solve the problem of gun homicides. Arguing against stricter gun-control measures, Representative Mike Rogers, Republican of Michigan and a former F.B.I. agent, said, “What the more realistic discussion is, ‘How do we target people with mental illness who use firearms?’ ” Robert A. Levy, chairman of the Cato Institute, told The New York Times: “To reduce the risk of multivictim violence, we would be better advised to focus on early detection and treatment of mental illness.”
But there is overwhelming epidemiological evidence that the vast majority of people with psychiatric disorders do not commit violent acts. Only about 4 percent of violence in the United States can be attributed to people with mental illness.
…Perhaps more significant, we are not very good at predicting who is likely to be dangerous in the future. According to Dr. Michael Stone, professor of clinical psychiatry at Columbia and an expert on mass murderers, “Most of these killers are young men who are not floridly psychotic. They tend to be paranoid loners who hold a grudge and are full of rage.”