No mission will go ahead without political decree, no matter how moral it may be.
Well, yes and no. My heartburn lies with the UN. One must only look to the Balkans in the past 18 years or so to see the UN has abdicated it's global responsibilities to regional entities such as NATO.
It's easier to turn a nation against a single "invader" than it might be to do so against "the world".
I understand the point you're trying to make, but the devil is in the details. Nations with polar opposite foreign policy goals in the UNSC are going to at a minimum barter their votes and at worst are going to veto anything they find counter to their goals. Think back to the physical absence of the Soviet ambassador during the vote over sending UN troops to Korea. Had the USSR not been boycotting the meetings, the UN resolution to provide military assistance to South Korea likely wouldn't have been approved.
I'll leave the morality of the war for others to argue, but only by the absence of one voting member of the UNSC did the will of the majority prevail.