There are lots of good arguments against the current military intervention in Libya and Michael Walzer sets some of them out in Dissent.
Arguments against ‘humanitarian intervention’ can usually be grouped under three headings: the pragmatic – what is our endgame; the pacific – people will be killed; and the ideological objections – which come from the right and left. Both of the latter have merits, although they self-evidently cannot both be true. They can be roughly summarized as ‘Why should western troops be asked to die for a cause that does not affect our ‘national interests’ and can we believe western governments when they say that they are in fact acting for altruistic motives?’
I find the latter of the three arguments the least interesting because they inevitably descend into a search for the hidden ‘real reasons’ for military interventions. While there is a place for such discussion, I think that the first two are more immediately compelling and would suggest that the case for or against a ‘humanitarian intervention’ rests on answering two broad questions: has the level of violence reached such a threshold that the use of counter-force is morally justifiable and is it a practical, strategic option that will actually make things better for the people concerned?