The odd part about US-UN relations is that any point in which the US has been in good relations with the US, it has been calling the shots often to its own advantage. In such cases the US has often managed to keep itself from being held to the standards that everyone else involved was expected to be held to. When we did give anything up, it was to keep the loyalty of allies during the Cold War. Now that we don't think we need our allies, we don't give anything up. But they are more assertive that we should.
In other words, the US has never really been a part of the UN except when dominating it. It would be better for everyone if the US left. Us because we'd no longer have to pretend that we care. Everyone else because they will learn to work together better without us trying to strongarm. In the longrun I hope to see the US see a need for good relations again and a new, better planned out international organization to replace the UN.

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"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside