Rarely, rarely...
Consider, for example, World War II:
(1) It was definitely a war of right vs. wrong, and of good vs. evil, in which there was no substitute for victory.
(2) But it also had its roots in the failure of the older politico-economic system: the mistakes made at Versailles, the failure to correct those mistakes in the following decade, and the failures of economic management that produced the Great Depression that rendered one-third of Germany's workforce unemployed and turned the Nazi Party from a joke into a dominant political force.
(3) And more important even than winning the war was winning the following peace: rebuilding Germany and Japan and integrating them into the society of the industrial democracies in such a way as to make a repetition of World War II inconceivable.
If you can't hold that complex a position, you don't have any business talking about World War II.
Similarly, today...
(1) Al Qaeda and the Taliban are malignant fucks, and there is no doubt that their fangs need to be pulled and that they need to be removed--even at substantial cost to innocents who just stand in the way...
(2) But Al Qaeda and the Taliban are now a problem in large part because of mistaken and misguided U.S. policies in the past, and because of the failures of modernization--democratization, industrialization, and secularization--in the Middle East.
(3) More important, even, than drawing Al-Qaeda's fangs (and getting a better government than the Taliban for Afghanistan, even acknowledging the Hobbesian point that any government is better than no government) is winning the peace: putting the Middle East on a track so that more Al-Qaeda's won't be hatched in the future and that the processes we think of as modernization--democratization, industrialization, and secularization--will roll forward successfully.
If you are too simpleminded to hold and agree with those three propositions, I don't think you have any business trying to do politics today--and I would apply this especially to George W. "I don't do nation-building" Bush.
Brad DeLong