Notice how France played the obstructionist role with Ethiopia and then totally capitulated in the ensuing war.
The second time was in the first Gulf War, right after the end of the cold war. The Soviet power still had to be respected, and the process gave us a way to get what we wanted with the Soviets going along.
There was some utility to the UN during the cold war, as it gave a way for the 2 opposing sides to have some dialogue with each other and was a vehicle that might not have existed had there been only embassies. But, the UN was set up in 1945 with rules that presupposed an alliance of the large powers with good will and common interest in world peace, and allowed some input from the lesser powers in the process. The cold war ensured that it would become a debating society for the most part, except with respect to some limited areas where both sides agreed.
After the cold war ended, there was some hope that the UN could fulfill more of its original goal of policing world conflicts where the US interest was not implicated. That did not come about, and in the age of terrorism, where the main role of the UN has been to hog-tie the US and limit its power, the UN is no longer either necessary, and is in fact, detrimental to US interests, insofar as its opposition to US policies causes useful idiots to oppose the war on terror at home and in allies.
The UN should be kept as a debating society, but the US should never again submit an issue with national security implications to the security council. New organizations, formed only with like-minded democracies, should be created over the next few year, which will be charged with the fight against terror and rogue states, and perhaps later, with taking care of horrible dictators who don't directly threaten us, like Mugabe.