Tyler Cowen has a post on the consequences of war in Iraq that makes, among other things, this point:
Today we see many signals that things are going badly. But most of those signals also imply that things would have gone very badly under the alternative scenario for Saddam's fall. A civil war, for instance, may well have happened anyway, albeit later.
The point here is that yes, the United States may well end up causing a full-blown civil war in Iraq. But if so, such a civil war might have happened eventually anyway, with or without a U.S. invasion, so this bad outcome shouldn't mean that the invasion of Iraq was therefore wrong. Well, it's true that civil war in Iraq might have happened no matter what. The United States made some particularly galling mistakes in the early days of the invasion and occupationnot providing security, disbanding the Baathist army, utter incompetence and fraud in the reconstruction processthat made the current mess more likely. But civil war might have happened no matter what the U.S. did. And it might have happened if the United States hadn't invaded.
But the overlooked factor here is what else the United States could have done had we not invaded Iraq. The opportunity costs seem just as important. We could have spent the energy and resources to securing loose nuclear material around the world, or promoting a peaceful democratic transition in a place like Egypt, or stopping genocide in Sudan. We've spent over $200 billion in Iraq; surely we could have found some humanitarian and freedom-enhancing use for that money elsewhere. In our alternate world, Iraq might still have descended into civil war anyway, after, say, Saddam Hussein diedwe'll never know of coursebut a bunch of other positive things would have happened too.