The UN acts as a way of us all keeping check on each other, not allowing any nation to become another Nazi Germany.
Are you kidding us with this?
The problem in Sudan is precisely the institutional state-sponsored genocide the Nazis were so famous for. The UN is allowing this right now, today. It allowed the same thing in Rwanda. It allowed the same thing in Iraq.
It is, in fact, a toothless organization that cannot keep its most powerful members in check, and refuses to keep in check anybody else. It serves only as a convenient mantle of fake legitimacy, something for a rogue state to drape around its shoulders when it can, and use for toilet paper when it no longer serves as a cloak.
If and when China makes its big play for world dominance, it will use the U.N. as a shield against all opposition. Should the U.N. stand against it, China will ignore it and carry on. And either way, China will put the U.N. at the top of its list of institutions to cast down.
China won't do this because it is an evil state. I don't believe that nations, or peoples, are inherently evil (though some governments and ideologies certainly can be). China will do this because this is the only practical course of action to take with the U.N.
I would say that the U.N. at least serves to limit any action, whether good or bad. I believe in the law of unintended consequences. I think that would be fine, if that's what the U.N. did. But in reality, it strives to limit the actions of the powerful, regardless of their morality, while turning a blind eye to the most horrible atrocities commited by the weak.
The U.N. is set up so that the worst human rights abusers can elect one of their own to chair the U.N.'s council on human rights abuses. And these people exploit this constantly. How can such an organization ever favor good over evil? It can't. At best, it can favor inaction over action, bureaucracy over diligence, corruption over responsibility.
Winston Churchill once said that democracy is the worst form of government known to man, except for all the other forms of government we know of.
Perhaps you're one of those who likes to despise the American system of government. Perhaps you ridicule the way the American people wield power. But if you dislike the kind of government the American system produces, consider this: the U.N. purports to be a world government, composed partly of freely-elected representatives, and partly of petty despots, dictators, and tyrants. Between these two choices, I'd have to say Churchill was right.