Robert Manne asks Will this war work?.

Perhaps the most relevant para is:

“Few principles are more fundamental to the conduct of international relations than the idea of non-interference in the internal affairs of sovereign states. Such a principle precluded international military action against even fouler tyrannies than Saddam’s – like Stalin’s or Pol Pot’s. If such a principle were ever to be revoked, it would certainly require general agreement between countries and strict provision for collective action through the United Nations. The international order would be thrown into chaos if individual countries came to believe that they possessed the right to take unilateral military action against what they judged to be an unacceptably tyrannical regime.”

I think the doctrine of non-interference has had its day. But Manne is right to point to the chaos that will arise if individual countries decide to appoint themselves as judge, jury and executioner in the affairs of others.