A Washington Post / MSNBC editorial by Michael Kelly lays out a Left wing moral cause for war.   He's mostly analyzing a recent New Republic (print) article by Jonathan Chait entitled "The Liberal Case for War"  The article is ok:

Chait begins by approvingly noting the three core liberal principles in foreign policy: advancing humanitarian goals, observing international law and acting in concert with international institutions. In each instance, he persuasively argues, the Bush administration’s policy [towards Iraq] meets the liberal test.

If those are really the core goals of "liberal" foreign policy principles, then maybe I'm far more of a lefty than I thought?   ;-)   However, I loved this little closing:

In the end, it comes to this: The anti-warriors of the left would rather see Iraq continue as a slave state under Saddam than concede any legitimacy to the idea of an American (or at least a Republican) use of force. It’s a price they are willing to pay. Because, you see, America is “a menace.” Well, it is a point of view. But you might have a hard time convincing the average Iraqi torture victim that it is a liberal one, or moral one.