The failure of the mental health system is a common thread through these killings. The lone apparent except is Las Vegas, but generally poor mental heath care and/or minding our neighbors seem to be a common thread.
James Holmes, the Colorado theater killer, is perhaps the best example. He tried to contact his psychiatrist while his tenure in a graduate program was falling apart. Other examples are less clear-cut since we know less about their psychological care and treatment. Jared Lochner, who killed a bunch of people, had been expelled from Pima Community College. Adam Lanza's schooling in an affluent Newtown, Connecticut should have exposed him to mental health professionals.
In an incident strikingly similar to the Texas massacre, Esteban Santiago killed six people at Fort Lauderdale International Airport in January 2017. His downward spiral is detailed here,
Fort Lauderdale shooter Esteban Santiago saw life falling apart. The article details how "a tape of a January 2016 domestic violence court hearing after his arrest for fighting with his girlfriend, a prosecutor lays out the case, explaining he broke down the bathroom door at Peterson’s home, then hit her in the head."
Kelley, the murderer in Texas, had similar domestic violence problems. They both had troubled military service.
De-institutionalization was a well-intentioned program. It was supposed to convert inhumane and, for the patient ineffective confinement into treatment in the community. This April 2, 1972 article, which I remembered reading, The Patients Can Walk Out At Any Time at Bronx State Mental Hospital
(link) made the case for de-institutionalization. Unfortunately few were as motivated as Israel Zwerling, and most looked at the process as a way of saving money.
The mental health system is not doing a good job of keeping these people under control. While the status quo ante before mass de-institutionalization was inhumane to the patients, it did keep the country safe from the lunatics. Perhaps the balance needs to be tipped more in favor of the public than the lunatics.
We can work at improving the humanity, and where appropriate the therapeutic nature of these centers. But we were safer with these people locked up than out loose.
But it doesn't stop at the mental health system; to some extent it involves a far wider community. People need to be more involved with their neighbors.
In recent years there have been plenty of mass shootings. In addition to those discussed about, there is Elliot Rodger (Santa Barbara) and Stephen Paddock (Las Vegas). All of these people were obviously troubled. All of these people, except maybe Adam Lanza, were in regular contact with other students, teachers and administrators at their respective schools. Dylan Roof was in regular contact with friends, roommates and his parents. The societal problem is that it is easier to ignore people who are not sociable and not pleasant to be with than to engage them.
With this horrific church massacre, we are treated to lectures about gun control and about racism. People forget that both in this episode and Sandy Hook parents without any apparent mental health pathologies were the ones that obtained the weapons, not the mentally ill adult-aged children. Guns are everywhere so efforts to control legally purchased guns are doomed to futility. The most those laws will do is prevent people who would hurt no one from owning a gun.
Racism is similarly rife in society. But no one things that Dylan Roof was active in any anti-black political movement.
I suppose that liberals don't want to deal with mental health issues because that would mean getting involved with and spending real time with unpleasant people who don't make good social companions. That takes real time and effort. Learning more about those people and having people who are conscious of their ups and downs might prevent some, though certainly not all tragedies.
I am not saying it is the role of untrained people to be psychologists. Far from it. But when people are left friendless for long periods, and no one reaches out to them a tragedy will sometimes occur. It is our job, as a society, to know our neighbors, students and colleagues.
I feel that forming real communities will solve some of these problems. Trying to remove the implements of crime from people who are far beyond obeying any law of any kind is futile and useless.
It is far easier and more satisfying to inveigh against guns and racism. It feels good and typical for liberals that's what matters as was pointed out here.