Dinesh D’Souza’s new book about President Obama is wrong in many ways. But its biggest error may be its premise.

The title of the book, The Roots of Obama’s Rage, makes as much sense as “The Roots of the Pope’s Atheism,” or “The Causes of Shakespeare’s Illiteracy.”

America wants to know not why Obama is so angry, but why Obama seems incapable of anger. Recent commentary has questioned not only whether Obama experiences ordinary emotions, but whether he is 1) a milquetoast, 2) an embarrassment, or 3) really a black man.

The notion of Obama as an angry black man in disguise, peddled during the 2008 election, has been thoroughly debunked. Many liberals believe Obama does not throw elbows because he does not want to jeopardize his tenuous hold on white voters. This may be true, but would it really upset white voters if the president showed anger at a massive oil spill in the Gulf of Mexico?

I think the primary reason the president never gets angry in public is that he does not believe anger is productive. Obama is a practical man. His foundational rock is not ideological but affective: He is reasonable and wants to be seen as reasonable. Hence his plea: “Can’t we disagree without being disagreeable?”

Reasonable people don’t harm common interests. “I’m not willing to let working families across this country become collateral damage for political warfare here in Washington,” Obama said this week as he gave up a campaign promise not to extend tax cuts for the wealthy, in exchange for extended unemployment benefits.

Obama represents a widespread pattern among liberals. Talk-radio experiments featuring left-wing ranters fail, even as there is insatiable appetite for right-wing fulmination. Given a choice between compromise and absolutism, reasonable people seek the middle ground. This is why many commentators see the Democratic Party as the party of compromise.

This is a grown-up attitude. If your neighbors blast loud music at 2 a.m., it may feel right—but isn’t reasonable—to aim giant speakers at their house and blast them out of bed at 4 a.m.

When scientists study different societies, groups with a higher percentage of reasonable people come out ahead of groups that have fewer reasonable people. But here’s the curious thing: Really successful societies always include people who sometimes act in angry, vindictive, and spiteful ways.

These people are not aberrations or cautionary signposts. They are essential. Get rid of them, and the group will function less well.

Take a common traffic scenario. Police cordon off a lane for road construction. They post signs a mile ahead of the roadblock telling drivers to merge into the remaining lane. The reasonable thing is to merge as quickly as possible. But this creates free passage in the blocked lane, and selfish drivers take advantage of the situation. They zip ahead of everyone else using the blocked lane. This makes the jam worse for everyone, because the sneaky cars merge close to the roadblock.

In a world of reasonable people, everyone would ignore the free riders. But in a world where some people are prone to vindictive anger, a driver might aggressively take matters into his own hands. He could move his car partly into the blocked lane in order to prevent others from racing ahead. He does this because he cannot stand to have others take advantage of him. The driver who acts in this way can be the recipient of violent road rage. He receives no thanks from anyone. But by deterring freeloaders, he can make the jam less onerous for everyone.

The Ultimatum Game is a laboratory experiment along the same lines: Here’s how it works: You and I have to divide $100. I get to pick first, and you are allowed only to accept or reject my offer. If I offer to give you $1 and keep $99, that isn’t fair. On the other hand, it isn’t reasonable for you to reject my offer, because that would mean neither of us gets anything. In a perfectly reasonable world, your getting $1 is better than your getting nothing.

Around the world, human beings do not act reasonably in this situation. They reject an unfair offer even if that means they get nothing.

Spiteful? Yes. Necessary? Yes. Knowing that people will sacrifice their interests—and the common interest—to enforce fairness prompts most people to offer a fair division in the first place.

In this way, spite is a form of altruism. It leads people to sacrifice their own well-being to enforce group norms. After the recent financial meltdown, there were people willing to let the global financial system collapse in order to punish the bankers who led us over the precipice. Obama, ever reasonable, helped the bankers to their feet because bringing them down would have brought all of us down, too.

The lesson of spite is not that people should always act unreasonably. Societies with lots of spiteful people do far worse than societies where most people act reasonably. But liberals are wrong to dismiss spite, anger, and the urge to retaliate as unsavory vestiges from our evolutionary past. Within limits, these emotions are salutary.

Debu Purohit, a marketing professor at Duke University, told me he used to have trouble persuading his daughter to get ready on time for school, which made him late for work. No matter how much she dallied, she knew Purohit was reasonable and would get her to class on time, even if that meant inconveniencing himself. So one day, instead of taking her to school, he took her to work with him—and then dropped her at school at 11 a.m., which got her in trouble. He never had to argue with her again about getting ready on time.

“You have to act slightly crazy to get them to believe you will follow through,” Purohit said.

Memo to Obama: Being unreasonable all the time is crazy, but if you’re always reasonable, you might as well hang a sign around your neck that says, “Exploit Me.”

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