Other libertarians, however, supported the war in Iraq because they viewed it as part of a larger war of self-defense against Islamic jihadists who were organizationally independent of any government. They viewed radical Islamic fundamentalism as resulting in part from the corrupt dictatorial regimes that inhabit the Middle East, which have effectively repressed indigenous democratic reformers. Although opposed to nation building generally, these libertarians believed that a strategy of fomenting democratic regimes in the Middle East, as was done in Germany and Japan after World War II, might well be the best way to take the fight to the enemy rather than solely trying to ward off the next attack.
Barnett is a subtle man when it comes to contract theory. It is therefore a bit sad that the rebuttal points are so obvious:
1. Overturning the Ba'athist regime couldn't be a war of any kind against Islamic jihadists, since they and it were enemies.
2. "Self-defence" must have some natural limits as a concept if it is to be a genuine limit on when violence is justified. One such limit is that the violence must be directed primarily against the person or persons who are aggressing against you. On Barnett's theory, killing a bunch of people unrelated to the act of aggression will cause a democratic revolution in the Middle East which will reduce the political appeal of the aggressing organizations. Even granting some reasonable probability that this will work, it isn't self-defence. It would be like attacking Tsarist Russia in the hope that it would undermine the possibility of the Bolshevik revolution. Even if the Bolsheviks would be a threat, this is just aggression.
3. The whole thing was a quadruple bank shot with a low prospect of working. It was far more likely that an unprovoked American assault on a Muslim country would increase support for jihadis, as has in fact happened. Democratic reform requires the solution of political problems that Western occupiers are powerless to solve and will likely make worse. Barnett ends with the lame "Bush screwed it up" line. Libertarians are supposed to realize that government policy will be implemented by imperfect bureaucrats. How people who think agriculture bureaucrats are clueless about farming can persuade themselves that unilingual ideologues unfamiliar with the difference between Shi'ite and Sunni will transform a foreign polity is beyond me.
4. Overthrowing the "corrupt dictatorial regimes that inhabit the Middle East" will not necessarily bring about "democratic reform". Whatever repression indigneous democrats face under Mubarak or the Saudi royal family is less than they will under what happens next. We can all take comfort from the end of the corrupt Shah and the repressive Hashemite rulers of Iraq.
5. Democratic reform, even assuming it was possible, would not make the West safer. Democracy means that the people get to decide what policies the state follows. When the people hate you, that's bad.
Update: Gene Healy, actual libertarian, takes Barnett apart here.