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.
This does not mean that mental illness is not a risk factor for violence. It is, but the risk is actually small. Only certain serious psychiatric illnesses are linked to an increased risk of violence...
I wrote on this subject yesterday. This is a longer and more detailed look at the general tendency to blame folks with psychiatric disabilities for more than their real share of violence in the US.
Americans shoot and maim or kill at extraordinarily high levels compared to citizens of other nations. However, the percentage of population with mental illnesses is not proportionately higher.