Brian Doherty’s history of libertarianism reminded me of a pattern that’s struck me before : When wars break out, there are far more doves who “sell out” and support the war than hawks who “sell out” and oppose the war.

Doherty mentions, for example, that when World War I began, anarchist Benjamin Tucker shocked everyone who still remembered he was alive by backing the French. And every historian of the era bemusedly explains how Marxist parties, supposedly united against their respective governments, suddenly discovered patriotism. For a more recent illustration, see the Iraq war. A bunch of libertarians angered their allies by supporting the war; how many conservatives angered their allies by opposing it?

But don’t hawks sometimes recant? Yes, but almost never at the outset. They gradually change their minds as hostilities drag on; they don’t have a sudden conversion experience when the shooting starts.

If I’m right about the facts, what’s the explanation? One story is that war raises the cost of pacifism. But which cost? People who say this usually seem to be thinking about the foreign policy cost. But as I’ve emphasized, one person’s pacifism is highly unlikely to change the outcome of a war, so in marginalist terms, it isn’t really a cost.

A much more reasonable interpretation of this story is that war raises the social ostracism costs of pacifism. People back wars once they break out because pacifists are a lot more likely to be spat upon for opposing the war that “our country” is currently fighting than they are to be spat upon for “opposing all war” during peacetime.

This needn’t imply cynical calculation; perhaps we’re evolved to sincerely support wars because during our evolutionary history, the tribe exiled or killed “conscientious objectors.” In short, perhaps early humans who lacked a “rally round the flag” response didn’t live long enough to become our ancestors. (That makes me a mutant. I can live with that.)

But why doesn’t the incentive/instinct to rally round the flag remain high at all times? There’s something very focal about the early stages of a war. Protesting a war the day it starts is a lot like announcing “I object” at a wedding; turning against a war after a couple years is a lot like waiting for a marriage to turn sour, and then confessing, “I never liked him.” In both cases, it takes an iron will to send the focal signal of opposition, and a lot less to send the weaker signal.

My colleague Robin Hanson has criticized those who think we have a hawkish bias. Perhaps it would be more precise to say that we are initially biased in a hawkish direction – and that, unfortunately, once we act on this bias, it is very hard to reverse course.