re: the UN and Spain
When the UN is in charge, it means it's not a specific country that takes the blame, but an international institution. This makes it a lot easier for every country taking part to the UN forces.
Another phrase for this is collectivism, or in the vernacular, "mob mentality," the idea that an act if done by one person is wrong, but when done by a group becomes somehow moral and validated. Some of the worst crimes in human history ride on this concept. Note the things that have been done in the name of "society" or "the people."
If it would be right for the United Nations to bomb, invade and occupy Iraq, it was right for the United States and its allies to do it. Unless objective standards don't count for anything.