There are two basic realities that get lost in this discussion.
The vast majority of people who have a major psychotic mental condition are not violent and do not harm other people.
The vast majority of people who own guns are not violent and do not harm other people.
One way or another people get killed by a gun in the US many times everyday. Much more infrequently there are incidents in which a group of people get killed in what appears to be an act of random irrational violence. When those widely publicized incidents happen there is usually some fairly definite evidence that the person committing the act had psychotic symptoms. Often they were already known to some mental health treatment service.
These incidents fuel the ongoing national debate about gun violence and what to do about it. The most recent incident at the Washington Navel Yard has heated it up again. Today's New York Times has two fairly useful articles on the topic.
There is the recurring notion that if we spent more money on mental health services we could eliminate much of the gun violence. There are also calls for stricter laws to restrict access to guns for persons with a history of mental illness. This runs up against the advocates of gun ownership who are opposed to any restrictions on what they consider a constitutional right to own a gun. These two opposing forces are caught up in the continuing political stalemate on the issue.
Another article gives us a notion of why mental health is not likely to have much impact on the prevention of gun violence.
In hindsight, it may seem clear that Aaron Alexis, who went on a shooting rampage at the Washington Navy Yard on Monday, posed a threat long before the attack, but most mental health experts say that barring the rare few who declare their intentions, it can be extremely difficult to pick out people who are likely to commit murder.
“Couldn’t someone have predicted this and intervened and saved all these lives?” said Jeffrey W. Swanson, a professor in psychiatry and behavioral sciences at Duke University. “I get asked this a lot when there’s a horrible mass shooting and indications that the perpetrator had a mental health problem. I can tell you the common characteristics of people who engage in mass shootings: It’s a picture of troubled, isolated young men that matches the picture of tens of thousands of other young men who will never do this.”I started out my working life as a social worker at a state mental hospital. There were people there who were violent and dangerous, but there were far more people who were completely harmless who had been shipped off simply because they didn't fit comfortably into the world around them. That was in the 1960s. Since then there has been a sustained trend of getting people out of such institutions and into the communities. That was supposed to be coupled with an adequate array of community support services. With the shrinkage of the social safety net those services have never been abundantly available.
As a result in that mass of seriously disadvantaged people that get lumped together as "the homeless", we see instances of people displaying fairly obvious symptoms of mental disturbance. People who have committed significant acts of violence in the past are likely at risk of doing so again in the future. However, as the above article points out, we lack the psychological technology to determine when people who have just shown strange behaviors are likely to become violent. There are important issues about the civil rights of people who have mental illness. Taking those away because a few of them will become violent is not a sound course of action.
Mental health services do have helpful things to offer to people who are experiencing mental and emotional difficulties. While medication and support services aren't cures in the sense of making basic problems go away, they can reduce the severity of symptoms and help people to deal with the world that they live in. Improving the nation's mental health system would not be a waste of money. The problem comes in trying to link this to gun violence. There is little reason to expect that it would eliminate the type of incidents that are creating the public outrage. Pointing the public concern in that direction is a convenient way to take the heat off the gun lobby.