Chelsea Clinton and leftist professor Corey Robin of Brooklyn College are mixing it up over the interpretation of Hannah Arendt. This might seem the very definition of a dogless fight for conservatives, but, setting aside the schadenfreude factor, it’s instructive nonetheless.

The dispute began when Clinton tweeted about a recent arson attack on an LGBT youth center in Phoenix. Her comment was: “The banality of evil.” Robin said she didn’t understand what Arendt meant by that phrase (which appears in the subtitle of her 1963 book Eichmann in Jerusalem), and it escalated from there.

Robin says Arendt’s point was that Adolf Eichmann, chief architect of the Holocaust, was not insane or super-brilliant or flamboyant or charismatic or even particularly zealous, just a time server with an unspeakably horrific job. Clinton, meanwhile, seems to interpret Arendt to say that in our modern world, the very idea of evil is becoming commonplace and banal.

Robin’s view is probably closer to what Arendt had in mind. The Phoenix arsonist, like many who commit acts of violence against the public, appears to have been just plain mentally disturbed rather than motivated by an overarching political worldview or pervasive atmosphere of hate and intolerance. Some people like to count up killers from the Left and the Right and see which is “responsible” for more deaths when, as Megan McArdle has pointed out, in many cases it’s hard to discern any consistent political viewpoint in an individual attacker, let along assign it to one side or the other.

The reality is that acts of mass violence are often perpetrated by people who are deeply troubled and acting on impulse, not rational actors pursuing an agenda. Corey Robin is right that the Phoenix arsonist was not an Eichmann-like figure, and Chelsea Clinton is right that we are becoming depressingly numb to this sort of thing. And it’s enlightening to watch them fight about it.