Also, the article states in the studies cited that it it's usually untreated schizophrenia coupled with substance abuse.

Universal healthcare would go along way toward addressing the "untreated" part of your criticism.

Mental illness means a lot of things catch up with me later and I will link some research that show amoung all cases of mental illness violence is less likely.

Ok. Let's run with that for a moment: mentally ill people commit less violence than mentally stable people. If that is the case, then "therapy" should increase rates of violence. If your thesis is correct, we should not treat mental illness, because doing so will increase violence.

Surely, you are not arguing for that absurdity. Surely, you agree that among those mentally ill people who do commit acts of violence, effective treatment should reduce the rate of such violence. Universal healthcare, then, addresses violence by providing broader access to such treatment.