Here's what we really know about gun violence.
In the case of mass shootings, the shooter is almost always male, and usually young. He has some identifiable problems fitting in, often has a history of mental illness. He can either pass a background check or can get hands on the guns of those who can. Usually, he finds in some ideology or crank theory a rationale for shooting people in a blaze of glory; sometimes that ideology is racist, sometimes it's religious, sometimes it's sexual, sometimes it's related to bullying. In any case, in his mind, he's going to do something about this thing that is preying on his mind.
Now, how you prevent his doing what he has decided to do, I don't know. But his particular pathology is not typical of all the other gun owners out there, or the other white people, the other Muslims, the other whatever they might be. Solutions that blame or inconvenience everybody else are not going to do anything about people like this. Guns are not the problem. White people are not the problem. All men are not the problem. Muslims are not the problem. The guy who doesn't fit in and has a bee in his bonnet: He is the problem. How do we identify him before he reaches this point? And what do we do with the not-yet-criminal without making everybody guilty until proven innocent?
And having said that, we are left to deal with the fact that homicides using long guns are actually very rare. Most gun homicides use handguns. And the typical gun violence in which most people stand a chance of being hurt or killed is committed in the inner city. African-Americans commit violent assaults at a far greater rate than white Americans, including those using guns. Why?
A book-length study just out traces the history of violence in America and identifies the Scotch-Irish/English borderers as the most violence-prone segment of society in early America. Touchy about honor, given to solving problems with violence, not trusting the police or society to enforce norms, disdainful of schooling, those we now call rednecks were quick on the trigger. In the transition to freedom, Blacks after the Civil War were not that way, but they learned from their white neighbors. Even as violence was visited upon them by Southern whites, so they too learned to be touchy about honor, to solve problems with violence, to not trust the police or society to enforce norms, to disdain school. Not all Blacks did this, of course; but as African-Americans from the South began to move north, their ways -- not only their violence, but their other cultural markers -- were disapproved of by their fellow African-Americans already living in the North. It is an irony that in certain corners of African-American society today, children are derided for "acting white" when the "Black" culture they are told to be loyal to owes so much to Southern white redneck culture.
Today, no social group -- not Whites, not Blacks, not Hispanics -- has a corner on violent behavior. But the cultural markers of redneckery that are more than two hundred years old are still going strong. In rural areas, it has some room to breathe, perhaps. It still holds people back, but in the less pressurized environment of the countryside it doesn't make the sirens go. But in the cities it festers.
At the same time there is among Whites and Blacks an absence of fathers in the cities, and an absence of other mentors who might shape young lives productively, give young people a place to belong, and set them up for success. So too many of them find their father-figures, their mentors, and their support system in the dysfunctional gangs, whose badge is hyper-sensitive redneckery (whatever color their skin might otherwise be).
Rebuilding a culture of marriage and fatherhood, acculturating boys and young men in ways that build up the community, learning to value education and respect those who know things and can do things, finding self-value in one's work, and most of all following the Way of Christ -- these are hard things to do, but we know how to do them. Why don't we? Because other solutions are easier. They may not work, but they assuage our guilt -- or our fears.
So: the common factor in mass shootings is the Oddball/Loner, but the common factor in the more usual gun violence is a breakdown in social norms (including basic relationships) and the adoption of ad hoc norms from our historically most violent social group. In both cases, passing laws or creating policy that intrudes upon the rights and habits of the law-abiding are not only annoying, but useless. We are looking for the keys we lost under the streetlight, not over in the dark where we dropped them.