It used to be that, every time a jihadi murdered a random crowd in one of the Western countries, all kinds of people would stand up and suggest that mental illness, and not Islamist ideology, was the cause—mental illness, because to say anything else might unleash a wave of bigotry against the entire Muslim universe. Barack Obama used to annoy me, years ago, with his insistence on presuming that each new terrorist who cried “Allahu akbar!” in the United States was somebody with mental-health issues. And yet, everyone knows that mental-health issues are not, by and large, the cause of jihadi violence. Islamist ideology is the cause.

On the other hand, some people do have a loose screw, and they commit massacres because of rage at their mothers-in-law, or something. Questions of psychotic derangement may be entirely relevant, in their case. Then again, still other people commit massacres on the basis of novel and colorful ideologies of their own invention. There is the example of the dreadful Anders Breivik of Norway, who killed a large number of people in 2011 on the basis of his own doctrine of Breivik-ism. And there is the example of the dreadful Dylann Roof, who, like Breivik, composed his own manifesto, which regretted that today’s Klu Klux Klan is not what it used to be, and called for a race war against blacks. Then again, there are mass murderers who collect guns and adopt uniforms for themselves, without ever going so far as to work up a doctrine and publish a manifesto—people who enjoy the benefits, as it were, of a suicidal and murderous ideology (namely, the opportunity to sport a natty uniform of some kind, and to go out and massacre random crowds), without having to do the hard work of mastering even the crudest of ideas. The entirely ideological jihadis who murdered the staff of Charlie Hebdo in Paris a couple of years ago took the trouble to don black uniforms, and so did the escapee from a psychiatric hospital who murdered the Texas church congregation just now.

Here, then, is a more-than-ideological epidemic. Only, what is ultimately its source? The original virus, the virus that is anterior to the proximate causes, whether ideological or pseudo-ideological or psychological—what can that original virus be?

I am entirely in favor of searching for the original virus. I have devoted years of my life to the search. The search for a virus is useful, it is good for the morale, it is bound to produce lesser insights of one sort or another, which may add up. But I suspect that, in the end, an original virus will never be found. Mass murder is the expression of frenzied rage, and nothing about frenzied rage requires special explanation. It is human to be peaceful and rational, but it is equally human to be frenzied and enraged. In neither instance is a virus required. Only, in that case, what we are to do about mass murderers?

I do not have a global answer—only the observation that, in New York last week, when a jihadi in a truck rammed to death eight people on a bicycle path and then leapt from his truck with a pellet gun and a paint-ball gun and yelled “Allahu akbar!,”  a policeman shot him. Did the policeman have a theory about the sources of mass violence? Perhaps not. But everyone is grateful that he had a gun.


Read more of Paul Berman’s political and cultural analyses for Tablet magazine here.