Brian Tamanaha at Balkinization thinks that the recent spat of neocon mea culpas over Iraq don't go far enough. He writes:
The first and overarching error of neoconservatives, Mr. Sullivan, is their willingness (nay, eagerness) to use war to achieve their ideological objectives. Neoconservatives see war as a tool, perhaps messy and unpleasant, not to mention expensive, but sometimes useful.
War is the greatest horror we inflict upon one another, destroying bodies and lives, inflicting untold pain, often on innocent bystanders. War must be a last resort, undertaken with great reluctance, when no other option is available--appropriate only when necessary to defend ourselves against an immediate aggressor (as international law recognizes).
(HT Mirror of Justice)
Broadly speaking, it seems to me that there are two arguments that could support Tamanaha's position. The first is some sort of Kantian duty never to do harm to others (except in particular circumstances like immediate self-defense) regardless of the consequences, which could include things like leaving a brutal and murderous regime in power. Notice, this argument is not based on any calculus of costs and benefits or means and ends.
The second argument would be that war never actually solves problems, but will only beget more violence and death. This is the more pragmatic intuition behind Sting's lines, "There's no such thing as a winnable war/It's the lie we don't believe any more." I actually think that this is the more interesting argument.
The neocons clearly did not subscribe to Sting's position. In so doing, it seems to me that they were inheritors of a peculiarly American strategic heritage. The fact of the matter is that through out its history America has been able to solve strategic problems through war. Indeed, America's wars -- with some notable exceptions like Korea, Vietnam, and the Gulf War -- have always resulted in a transformed world where the old threats and problems simply no longer existed. Contrast this to the European experience, where wars routinely left precisely the same strategic situation in place that called them into being. The most dramatic example of this was World War I, which began with a resentful and ultimately expansionist Germany surrounded by anxious powers, and ended with a resentful and ultimately expansionist Germany surrounded by anxious powers. However, lesser examples abound, e.g. the Peace of Utrecht, the Peace of Augsburg, the Peace of Paris, etc. all of which left the same balance-of-power system in place that had led to war to begin with.
Ironically, World War II is the war that fixed the American and European views of war. In European eyes it is the holocaust that showed that war just doesn't work. In American eyes it is the evidence that American strength has the ability to solve even the most intractable of strategic problems, namely the centuries of bloody balance of power war making in Europe.
I think that both the American and European view of war are wrong. Tamanaha is surely right that war is a horrible catastrophe. On the other hand, I am not convinced that it is the worse catastrophe that could befall someone, and I don't think that the universe of things worse than war is exhausted by immediate threats to one's own safety. Yet the neocons have clearly been seduced by America's history of military successes, viewing the inconclusive wars of the second half of the 20th century as aberrations from the norm. The fact is that war is always a dangerous and terribly costly tool. Sometimes it will work, and sometimes it will not, and one needs more than good intentions to decide which case is which.