Acts of evil always puzzle civilized people because they cut against the grain of what we all believe: that violence against innocents breaks the bonds of basic humanity. That means that when we see an act of evil, we have a tendency to simply label it “other” and then to dismiss it as out-of-the-norm. Here, for example, is National Review’s Jim Geraghty, with whom I usually agree:

We’re going to hear a lot of questions in the coming days about “why did he do it?” Does it matter? Aren’t all of these shooters more or less the same? In their minds, they’ve been wronged by the world; the world owed them something and it refused to give it to them.
That’s certainly true. But not all evil is the same, at least in terms of how we fight it. Yes, all evil people feel aggrieved. But that’s not enough – lots of non-evil people feel aggrieved, too, sometimes correctly.

A good framework for examining evil comes from psychologist Roy Baumeister. In his book Evil: Inside Human Violence And Cruelty, Baumeister breaks down four types of evil.

1. Instrumentality: The notion that evil acts aren’t evil so long as you’re performing them with a good end in mind. This would include the suicide bomber, who believes that he’s changing the world for the better by slaughtering children in pizzerias, or the dictator who slaughters his enemies in pursuit of power.

2. Threatened Egotism. Baumeister found that violence wasn’t perpetrated by those with low self-esteem, but those with self-esteem that was threatened. He found that “violence is perpetrated by a subset of people who think well of themselves, and indeed it mainly occurs when they believe that their favorable images of self have been threatened or attacked.” This is the danger inherent in, for example, the microaggressions culture that suggests threat where none exists.

3. Idealism. This is really just a subset of instrumentality. It’s the belief that your violence makes the world a better place by drawing us closer to utopia. The worst wars in world history have been caused by idealism, as Karl Popper suggested.

4. Sadism. This is the last and least common type of evil. Baumeister wondered if it even existed for years; only later did he say that it existed in some types. His theory is that guilt prevents us from enjoying violence, but that when our guilt is assuaged, violence and evil can become fun.

This neglects a fifth type of evil, because we don’t really consider it evil: mental illness. That’s been a serious factor in mass shootings throughout the United States.

Why bother with this taxonomy of evil? Because we fight each type of evil in a different way. It’s easiest to fight the connection between mental illness and violence by quickly moving to separate the diagnosed mentally ill from weapons, for example. And sadists often show themselves early, too. But Baumeister’s other three types of evil are difficult to identify, because we can all fall into them. That means the only good policy would be prevention in the form of moral education — or, perhaps, in fighting importation of evil alien ideologies in the case of idealistic evil (as, for example, radical Islam). And that’s a deep and uncomfortable topic for most people, who prefer to see evil as something alien, and therefore easily tackled by public policy.