Like many people, I was horrified by the largest mass shooting in U.S. history. It had a particularly strong impact because I just finished a three-day vacation from paying attention to the news, which was already depressing in large part because the presidential election had been reduced to a choice between a champion of policies that are making our planet uninhabitable, and a megalomaniac who likely would speed up our demise.
Readers of my work know that I respond to emotional discomfort by attempting to understand the triggers, typically using abstractions that I invent based on experience and extensive study. Luckily I already had a basis for understanding, in the form of what I call "group interaction." Of the three types of interaction I identified (isolation, domination, and coexistence), domination seems to be preferred by mass murderers since its goal is total elimination of other groups of people.
The shooting added some momentum to the ongoing debate about guns; and here, too, my research provides some insight. Guns provide an unfair advantage to small groups, down to the individual level, in effectively stealing resources from other groups to advance their own growth. A "fair advantage," on the other hand, would be to allow motivation and population to determine the outcome of an interaction, which in practical terms would mean letting everyone have access to the same technologies. Resistance to gun availability might thus be explained as a group's fear of granting unfair advantage on one or more other groups; and the focus of such fear on government intervention might be symptomatic of isolationist preferences by people who see themselves as significantly different from those represented by the government.
The preference for isolation is a good candidate for explaining parallel debates relating to immigration and race. If people fear they will lose resources if people from another group merges with theirs, then they will try to avoid the merger. This is especially likely if the other group has apparently far fewer resources than they do, because the other group would be more motivated to take resources from them.
Those of us who favor coexistence have trouble understanding these debates, perhaps because we tend to have a very fluid identification with groups, easily changing the definition of our group to include the sum of others. I personally have no problem considering the entirety of humanity as the basis for my identity, and then shifting with understanding and familiarity to a broader identification with the rest of life on Earth. It is inconceivable that deadly force would be justified except in cases of direct threat, so its use is especially shocking.
That said, I doubt any of us is pure in identity with groups and our interaction preferences, either collectively or as individuals. For example, I expect that all of us (myself included) favor our families over other people for primarily biological reasons, with shifting degrees of allegiance to individuals based on experience and natural similarities. We have a drive to meet basic needs, for ourselves first and our self-identified groups as a close second, which includes assessment of the potential for growth in population and resource consumption. There are also situational considerations, like joining a company as an employee, and facing existential threats such as natural disasters and predation by other species. Someone who coexists as a matter of preference (like personality) may freely practice it with family and friends, but be forced to take resources from others as a requirement for meeting needs as part of a corporation seeking economic hegemony. Knowing this, I try to treat each interaction and perception of group identity as parts of a transient event, useful in the moment but subject to change without warning, which is my intellectual argument for broadening definitions as much as I do, as well as adapting to my own acknowledged ignorance about most things.
Based on my research, the most reliable way to avoid lethal violence is to have a access to a large amount of resources that is not controlled by anyone else (and can't by its nature be controlled by any person or group), and that requires cooperation to acquire and process into needs and wants such as artificial environments. Such a situation has been extremely rare, and may be practically impossible now that humanity has merged both as a collection of groups, and (mostly by domination) as a species with the group representing our planet's other species that is also its primary set of resources. There may be an exception for a tiny minority of us who escape into space and approximate the ideal situation for a while, but I fear that the overwhelming majority of us are doomed to imminent painful and lethal collapse that will make our current gun violence look trivial by comparison.