After two women trying to inoculate Pakistani children against polio were shot this week, some news accounts were quick to place blame: "Anti-polio workers started being attacked after a Pakistani doctor, Shakeel Afridi, ran a fake polio campaign in the city of Abbottabad to help the United States track down Osama bin Laden," reported NBC News. The World Health Organization, which employed the women — one of whom died — reports that 18 of its workers or their bodyguards have been slain since last July.
Actually, Afridi's campaign involved vaccination against hepatitis B, not polio, but that distinction has been lost amid rising resistance in North and South Waziristan. "Polio is the vaccine with a long history of controversy among Muslims in many countries," The New York Times reported last year, "so Pakistanis who were not familiar with the difference turned on polio vaccinators."
What we are seeing here, as critics of the tactic have pointed out, is an example of the law of unintended consequences. We spend a great deal of energy either denying or pretending we can evade this law, when instead we should be embracing it. At its core is a sensible call for modesty about our ability to predict the results of our preferred policies.
The law of unintended consequences rests on a deceptively simple insight: We can't predict the future. There are always externalities, and it's impossible to identify all of them in advance.
Sometimes the consequences are vast. When Eli Whitney patented the cotton gin in 1794, he couldn't have guessed that the result would be a sharp increase in the number of slaves; many authorities think that he expected the opposite. Certainly he would not have imagined that, generations later, historians would cite his invention as one of the precipitating causes of the Civil War.
In our sillier political moments — that is, most of our political moments — we talk as though it isn't possible for good ideas to cause any bad results. If it's our program, then its only results are good ones. That's why many supporters of the Affordable Care Act insist that their beloved statute isn't having a depressing effect on hiring — surely nefarious employers are to blame! And why many supporters of our drone-attack strategy against terror leaders reject the accusation that we might be creating more terrorists — they'd become terrorists anyway!
Surely a more mature form of reasoning is to concede that whatever policy we support will have bad effects as well as good, and that we take the positions that we do because we believe that the good effects greatly outweigh the bad.
Unintended consequences may, of course, be positive as well as negative. For example, Adam Smith's metaphor of the "invisible hand" is the unintended consequence of countless small decisions by people seeking to maximize their individual welfare. Indeed, as the political theorist Christopher J. Berry reminds us in the "Oxford Handbook of Adam Smith," for Smith and his fellow intellectuals of the Scottish Enlightenment, the unintended consequence was seen as more important than reasoned deliberation in driving social change. This model of spontaneous ordering, still popular in some circles, holds that our blindness about the future should make us appropriately humble about what we can accomplish by reasoned action.
Few thinkers devoted more energy to the problem of unintended consequences than the great economist Albert O. Hirschman, who died last year at 97. By no means a conservative — in fact he was a proponent of liberal interventions of many sorts — Hirschman stands as perhaps the most eloquent advocate of caution in public policy.
In his massive but fast-paced new biography of Hirschman, the historian Jeremy Adelman shows Hirschman's gradual disillusionment with grand development plans of the kind that he had once championed. He came to realize that an oppressive regime could readily turn them against the very people they were intended to help.
Hirschman, an escapee from Nazi Germany, worried all his life about the pernicious consequences that arise when governments are certain that they are right. He eventually became a crusader for the proposition that social scientists had an obligation to consider the likely real-world effects of their ideas, rather than remaining "cozily ensconced" behind walls of theory. Economists in particular should face up to the consequences of what their work had "at least helped bring about."
Policy makers and pundits could also profit from this advice. One way of prodding our political debates toward seriousness is to stop pretending that any idea, no matter how well-intentioned, will have only beneficial effects. The more complex the policy in question, the more likely are unintended consequences.
Let's return for a moment to the anti-hepatitis campaign that served as cover for the search for bin Laden. In at least two important ways, it was a success: It surely helped the U.S. kill bin Laden, and it vaccinated many thousands of children. It also resulted in the imprisonment of Afridi, the courageous physician recruited by U.S. intelligence. His 33-year sentence is another unintended consequence.
Hirschman was right: When our policy choices cause real harm, we shouldn't turn away from what we've wrought. So the Obama administration, having made the choices that put Afridi behind bars, should face up to this fact, and try harder to get him out.
(Stephen L. Carter is a Bloomberg View columnist and a professor of law at Yale University. He is the author of "The Violence of Peace: America's Wars in the Age of Obama," and the novel "The Impeachment of Abraham Lincoln.")