Actually, I think the UN Security Council doesn't care one bit about what's in the national security interests of the United States. They reacted in the Afghanistan instance, because they all, particularly Russia, had experience with terrorists on their own soil and taking on the terrorists after 9/11 was in the security interests of the world, not just the US. The UN Security Council, on a regular basis, ignores the interests of the US and the west in general. The Chinese and Russians have their veto card in their hands ready to wave all the time.
GWB made it clear that the national interests of the United States were not dependent upon the good will of the UN - he would act, whether the UN approved it or not. America's true friends acted with America in Iraq.
As I've said on many occasions, I'd love to see Canada tell the UN to go **** themselves, take our dues and other supports for that useless, corrupt body, and join the US and other like minded democratic nations in a similar, more useful, more morally justifiable body.