If we cast a wider net and examine violence more broadly, evidence suggests mental illness does not cause violence. Large epidemiological studies have shown that rates of violence among people with mild-to-moderate mental illnesses range from 2%–4%, compared to 1%-3% in the general population. One of the strongest longitudinal studies, called the MacArthur Violence Risk Assessment Study, found that only 1% of patients discharged from psychiatric facilities committed an act of violence against a stranger with a gun.
So not all mass shooters have mental illnesses. And the overwhelming majority of people with mental illness will not commit mass murder (or violence in general). This suggests that other factors are more important in predicting mass violence. Experts believe the following factors, especially in combination, are more predictive:
a/ Particular motivations, such as revenge or envy. A type of mass murderer identified by some experts is the “pseudocommando,” who “kills in public during the daytime, plans [the] offense well in advance, . . . comes prepared with a powerful arsenal of weapons,” expects to die during the massacre, and is driven by intense anger, resentment, and revenge.
b/ Adoption of extremist beliefs that promote the use of violence to attain one’s goals. There is a growing concern in the U.S. about the rise of extremist groups and influences and their relationship to mass killings.
c/ Social isolation. When people with these and other characteristics that put them at risk for violence become socially isolated, the combination can place them at even greater risk.
Whether one terms these characteristics dysfunction or evil, such behaviors do not constitute a diagnosable and treatable health condition.
A research group studying mass shootings for decades (called The Violence Project) concluded that mass shootings are largely the results of a constellation of behaviors involving a buildup of childhood trauma, an identifiable crisis point (separate from psychosis), the need to blame someone, and the opportunity to conduct a mass shooting (i.e. access to firearms).
Blaming mental illness entirely “conceals it more than it reveals it.”Source: Katelyn Jetelina