In a perfect world, I would agree. However, our enemies would love us to leave the UN because then we would loose our veto. I could see the EU gaining the use of our veto. You then would have the 6 permanent members of the UN passing world wide resolutions against the US and her allies. Not a good scenario. The United States must stay in the UN.
The earth didn't stop rotating when the League of Nations came to an end. And it won't when the U.N. comes to an end.