I wrote in a previous post about the importance of realism in foreign policy. I'm indebted to John Lukacs, in his excellent new book on George Kennan, for a somewhat more sophisticated discussion that I'm happy to lift in its entirety for your delectation He speaks of scholars who:
"were wont to contrast Kennan [who criticized the "legalistic-moralistic" approach] 'the realist' to the 'idealist' category of American foreign policymakers. One half of that fixation is correct, but the other half is not. 'Moral' and 'ethical' are not quite the same things. Perhaps he should have coined the term 'legalistic-moralizing' rather than 'legalistic-moralistic,' but that is not the main issue. Kennan's view of foreign policy and of the world and indeed of human nature was a moral one. And the American predicament, to this day, is the failure to understand that the opposite of idealism is materialism, not realism; indeed, that idealism and realism are the best possible combination; that history is made by what people think and believe and that the entire material organization of the world is but the superstructure, a consequence of that."
I recommend the entire book highly.