Yeah, but there is difficulties about state sovereignty issues as you point out with regard to client (or even just supportive) states. Notoriously both China and the United States were unwilling to do anything about Pol Pot, until Vietnam said "screw this, we're going in regardless of what the Security Council" says... and I suppose that does become the issue at stake. Countries which are the power brokers on the Security Council determine for themselves what is, and isn't, a mass atrocity (e.g., Russia in Grozny).

The principle of humanitarian intervention seems sound enough. The fog of war clouds responsibilities. And the structure of the United Nations ensures a balance of powers rather than principled decision making - and all of this is beside the point you make about having a new government that seems to have a modicum of stability and legitimacy (although both Bosnia and Timor-Leste seem to have come out OK with this, Libya is perhaps too early to tell).