The Founding Fathers created the "beyond a reasonable doubt" standard to protect us from arbitrary denial of our freedoms. That the motivation is not to punish doesn't change the effect on the individual, the denial of freedom. So the standard "not dangerously insane until proven dangerously insane" should be used and that standard is lagging currently. The exact same burden of proof ought to be used and the person should be entitled to a full jury trial. Locking up a bunch of sane or harmless mentally ill in order to reduce violence isn't worth it.
We also have to be careful about what we really know. People will read things in the media and then pretend to just know things. Stop and think "where did I learn that from?" Mental illnesses often have shockingly broad criteria if you read about them. Parents eager to avoid responsibility look for labels for their children, children internalize the labels, believe it is then, surrender to it. We may be making "mental illness" in some individuals or exacerbating it by suggesting they are mentally ill. Beliefs are powerful and can rewire the brain given enough time. Look at those commercials on TV pushing antidepressants and showing happy, carefree people. They deliberately try to recruit people who have the blues over to thinking they have major depression. Another problem with current psychiatry is the overfocus on brain chemistry. Recently a psychiatrist had a brain scan done and found that it looked the same as a psychopath. That doesn't mean that the psychiatrist is a psychopath(unless we are defining the term based on brain chemistry, but then the implication would be that a person can be a good psychopath and it's not automatically a disorder), it means that likely psychopathy is not genetic or biological, rather a personality type, a sort of ruthless go-getter personality type when exposed to bad environmental influences channels their drive and ambition into evil pursuits, with the implication that the same sort of chemistry under completely different circumstances could even yield a saint. Further implication is what if the brain chemistry underlying depression is not in fact for depression but is for some personality type that under exposure to current social conditions tends towards depression? Psychiatric researchers wrongfully conclude any time a study is taken on brain chemistry that the brain chemistry is the direct cause rather than indirect. This assumption is made in spite of the evidence leaving open the indirect cause possibility and since it won't make money for Big Pharma if it turns out to be indirect because then people will have to deal with their problems the old-fashioned way instead of trying to change themselves with pills, then the psychiatric researchers are unlikely to undertake any amount of studies in order to tell whether it's direct or indirect. It's easier for their careers and money to just assume it's direct.
Anything that would improve the mental health system would also reduce violence. But we need much more than that to reduce violence. We can't just react to the assaults that are done by mentally ill people and consider the case closed. Our society is far too violent, and either we are all mentally ill, or mental illness is not the root cause. I tend to think of violence as a social disease, and think that we need to address the illness on a community level.
We have a woefully funded mental health system, and a lot of people slip through the cracks. These people that go on shooting rampages obviously have something severely wrong with them, and more than one has been diagnosed with a serious mental illness.
Perhaps if we had a system that was better equipped to give them therapy and life coaching, part of that meaning we make our mental health laws more robust and comprehensive, we would have less violence due to mental health issues.
Violence in the United States of America is one of our largest societal issues. It is fair for us as a country to want to focus on minimizing this violence as much as possible. With violence having much of its roots in mental illness, it is only logical to want to combat violence through the use of mental health laws.
To think that all violence is rooted in mental health problems is both presumptuous and incorrect. While mental illness is a large problem in this country, there are more constructive ways to combat violence aside from making mental health the main focus. Violent television for example could be looked at a bit more closely.