Maggie Gallagher sums up why the UN is not (and probably cannot be) the moral voice of the international community:
We stopped short at the Kuwaiti border last time because that is what the United Nations wanted us to do. U.N. mandates are not concerned about the fate of the Iraqi people. Once the aggression against Kuwait was repelled, the United Nations was satisfied. Bush the elder knew that pushing forward to Baghdad would have sparked international outrage, as this war has.
The United Nations is a collection of states, not a creation of the people. It reflects above all the interests of those in power, which means the right to stay, unmolested, in power. The United Nations exists to protect borders of existing states — the good, the bad and the very, very ugly.