On the contrary, there are PLENTY of fiascos that have been committed via the auspices of the UN with the full support of the US. In fact, FAR more often than not, it is the United States leading the charge, rather than exercising it's veto power. The Korean War, that mess in Somalia, and the Gulf War are just a few examples - and that's just off the top of my head. So I ask again: what are your counter-examples? What things like this have been averted because of our veto power?
But what is even more ridiculous is your implicit assumption that the globocrats in Washington D.C. will even WANT to "keep the UN in check." That is an exremely foolish & utterly unfounded assumption. At best, it is wishful thinking and is completely detached from reality. On the one hand, the neo-con types want to use the UN as a rubber stamp to confer the illusion of legitimacy upon their bloody, evil schemes (such as the aforementioned Gulf War). On the other hand, the progressive types want to use the UN to destroy US sovereignty and to plump for their fantasy of "one-world government".
The fact is that the UN is nothing more than a platform for grandstanding globocrats. Whatever power the UN wields derives largely from the participation of the US in the UN. The best way to undermine the UN is NOT to participate in it. The best way to undermine the UN is to destroy it's appearance of legitimacy. If the most powerful empire in the entire history of the world tells the UN to go to hell, what is the UN or its other members going to do about it (other than splutter with useless outrage)?
I asked you before if you remember the League of Nations. Do you? The United States was not a member. It was a toothless flop. There is no reason to think the UN would be any different.
Withdrawing from the UN is a VERY good idea and we should do it. Unfortunately, however, there is not even the slightest chance in hell that it will actually happen any time soon.