Young Ezra Klein makes a good point:
What I want is not a foreign policy vision that builds from a foundation of values, but from one of consequences. Whether a policy is concordant with America’s view of itself is less important than its likely outcomes. The Paul Wolfowitzes of the world had thought plenty about values and were perfectly capable of discussing their vision of Iraq as a shining city on a Mesopotamian hill. What they hadn’t thought about were outcomes — constraints on our action and capabilities, the likely effects on others’ actions of our use of force, etc. Good thing they weren’t really pressed on the subject, lest they’d have had to conjure up a postwar plan for a reception that didn’t include candy and flowers — a plan they didn’t have. But they weren’t questioned, because they were effectively able to keep the conversation focused on values — do you care about liberty? hate tyranny? believe Arabs can be democratic? — rather than consequences.
I believe, however, that it is strictly forbidden to make this point without citing Max Weber’s “Politics as a Vocation”. What Ezra is complaining about is the need for US foreign policy to be guided by an ethic of responsibility focused on whether or not our actions will, say, lead to massive chaos and bloodshed rather than a focus on “moral clarity” or whether or not our policy proposals are, in some sense, grounded in high ideals.