Perhaps people are bored with this question, so I'll put the main discussion below the fold, but Jacob Weisberg has an article out on the "Incompetence Dodge" issue in which he kindly links to the piece Sam and I wrote on this some time ago. As Weisberg says "What makes this backward-looking conversation more than academic is its implications for American foreign policy beyond Iraq." He disagrees with my take on this, but it's not really clear to me from his article why he disagrees with me other than that he seems to think that if he agrees with me that means he must be an "isolationist" and he doesn't want to be an isolationist.
The difference between Kosovo and Iraq isn't between a country that wanted peace and one that didn't. It was a matter of better management and better luck. To assume that American intervention can't work ignores the relative success of recent "wars of choice" in Bosnia and Kosovo (leaving aside the more debatable propositions of Somalia, Haiti, and Panama).
Like many observers, it's not clear to me that Weisberg is aware of the situation in Kosovo. The difference between Kosovo and Iraq isn't the difference between a peaceful country and a non-peaceful one, the difference is that we don't really care about violence being perpetrated against Kosovar Serbs. See here for a March 2004 report on anti-Serb violence in Kosovo. Just last week, the NATO peacekeeping force decided it needed a surge of troops to the north of the province to bring security to mostly-Serb areas. The point here isn't just to carp, but that one needs to understand what actually happened in the past to draw lessons from it. Intervening in Serbia's war against Albanian separatists in Kosovo succeeded in kicking Serbian military forces out of Kosovo, establishing Kosovo's de facto independence, and putting it on a path to de jure independence at whatever moment the international community decides they're willing to accept it. It didn't succeed in turning Kosovo into a stable liberal democracy or in establishing harmony between its ethnic groups.
Back to Weisberg:
Rumsfeld's Pentagon and Cheney's White House simply rejected the idea of planning for a hostile occupation. They disregarded basic counterinsurgency theory, which suggests that you need to send 20 troops for every 1,000 civilians to ensure order and that the occupiers need to operate with a light hand to win hearts and minds. In Iraq, that would have amounted to something like 450,000 troops, if you exclude friendly Kurdistan.
Now as we noted in the article, the United States Army lacks the capacity to sustain a multi-year foreign deployment of 450,000 soldiers. Not even close. Even if you can't on some help from the Marines and the United Kingdom, you're nowhere near the neighborhood. What's more, as we also noted in the initial article, the fact that people keep making this argument even though it would be very simple to check and see whether or not 450,000 soldiers were available is telling. It's also worth noting that the liberal hawk CW on this point is purely post hoc. In 2003, Kenneth Pollack and Daniel Bynum argued (PDF) that "By leading a multinational force of initially at least 100,000 troops with a strong mandate to act throughout Iraq, the United States and its coalition partners will have an excellent prospect of ensuring the degree of security necessary for a successful transition to democracy."
Beyond this, it's not clear that the Bosnia and Kosovo precedents from which the 20:1,000 ratio and general optimism about nation-building are drawn are all that relevant. Kosovo I discussed earlier. In Bosnia, what peacekeepers did was take ethnic populations that had already been physically separated and essentially helped police the boundaries between them. The goal in Iraq was to build a unified, pluralistic liberal democracy. We haven't succeeded in doing that in Bosnia or in Kosovo, so neither Bosnia nor Kosovo can be considered evidence that we could have succeeded in Iraq. Relatedly, Weisberg argues:
As Iraq descended into mayhem, a disengaged president continued to put forth the absurdist goal of establishing liberal democracy in a catastrophically damaged country where it had no root.
This is no fair. Establishing a liberal democracy in Iraq was absurd but it was the mission. You can't argue that the mission wasn't doomed to failure and only failed because of incompetence, and then cite as an example of incompetence the national leadership's pursuit of the mission objectives. Yes, yes, a smarter, wiser president could have invaded Iraq and made things turn out less bad. The question on the table, however, is whether "competent" execution of the invade-occupy-democratize plan could have achieved the goals of the plan.