I think one reason that many in the West are so enamored of the United Nations is that they view it as the ultimate democracy: a global town hall, where each nation gets an equal say in the General Assembly, regardless of size, population or wealth (the Security Council is decidedly less democratic, but that's another story).
But is that a good thing? The U.N. has a charter, and its purpose is to promote liberty, human rights, and tolerance, not simple majority rule for the international community. I think it's reasonable to demand that member states demonstrate at least minimal adherence to the principles set forth in the U.N. charter as a precondition for inclusion.
What purpose is served by allowing Sudan to have voting membership at all? Are we really to believe that the Sudanese delegation is in any way representative of the will of the Sudanese people? How many delegates to the U.N. are there representing governments that came to power simply by being the toughest thug on the block? To confer legitimacy on these nations, and to grant them the same influence as, say, Belgium (don't ask why, I just picked it), makes a mockery of everything the U.N. supposedly stands for.
One can legitimately ask why we need the U.N. at all, at least in its current form. Its advocates present us with a false choice between the current world body on the one hand, and rampant, reckless, unilateralism on the other. But alliances and coalitions of nations have always banded together to address international crises. They have done so long before the advent of the U.N., and would continue to do so if the U.N. were to magically disappear tomorrow.
Indeed, the U.N. was founded around just such an alliance -- the victors of World War II. The problem is that the makeup of the Security Council is frozen in time to reflect an alliance that arose to face a specific threat more than half a century ago. One of the five permanent member nations no longer even exists (the Soviet Union), and probably shouldn't have been included in the first place. They were only an "ally" because the Germans betrayed them. Up until that time, they were a happy member of the "Evil-Dictators-Taking-over-the-World" club. The UNSC is an anachronism. Why China and not Japan? Why Russia and not India? Why France and not Germany? The current structure is, at best, an anachronism. These are fundamental, structural problems, above and beyond the widespread corruption we're seeing again with the "oil for food" program.
So should the U.N. reform itself? Only if it means to be taken seriously.