Many economists (not all) might agree that it would be lovely if we lived in an Edenic utopia in which everyone did the best for society without thought of themselves. But almost all economists recognize that self-interest is a powerful force that must be dealt with, and therefore that economic policy must be designed on the assumption that people will try to maximise their own good, rather than society’s. Similarly, foreign policy assumes that states will act in their own interest, and try to design a foreign policy that works within that constraint [bold mine-DL]. The netroots (and many libertarians), who have a more idealistic theoretical model, are outraged. They are particularly outraged because they see that in certain cases, such as Iraq, their prescription would have produced a better outcome. ~Megan McArdle

First, foreign policy does not assume this, but traditional foreign policy realists assume this.  It remains unclear to me how accepting that states act out of self-interest requires anyone to endorse interventionist foreign policy prescriptions or the rather open-ended ” war for vital interests, whatever they may be” position.  It is not clear to me that people who object to wars of aggression are espousing an “idealistic” worldview, unless we would like to say now that only “idealists” are interested in opposing the principal crime for which the war criminals at Nuremberg were executed.  Undoubtedly, all states operate out of their self-interest.  One of the basic red lines of international law, of the international system itself, is that no state should be able to pursue that self-interest through an aggressive war.  It was to provide a mechanism to prevent such acts, theoretically, that international organisations such as the U.N. were created in the first place.  Respecting the sovereignty of other states is one of the bonds that is supposed to hold the international state system together.  Apparently, Drezner believes that the Foreign Policy Community generally agrees that this rule does not apply to the United States. 

The formulation of which Drezner approves declares that the interests of some states or perhaps just one state take precedence over the constraints of that system.  If this were an economic model, it would be a near-monopolistic system in which the monopolist is allowed to steal and destroy the property of everyone else if he has a “vital” need to do so.  It is curious that Drezner would basically confirm the worst possible indictment of the Foreign Policy Community, which is that it is fundamentally biased in favour of illegal and aggressive warfare, but he seems to have done just that.