Andrew Sullivan and Thomas Friedman have both come out in favor of a "mend it, don't end it" approach to the UN. Sullivan suggests, approvingly, that US Secretary of State Colin Powell's newfound militance regarding Iraq "is as much about rescuing the U.N. as it is about protecting Western citizens from Saddam's nerve gas." Friedman argues for replacing France with India in the Security Council, because "India is just so much more serious than France these days", particularly with respect to Iraq.
Multilateralism is like "world peace" or any other unrealistic ideal: everyone pays lip service to it, but most people embrace it precisely to the extent that it advances their own goals and interests, and are happy to discard it when it becomes inconvenient. The French and German governments, for instance, are quite fond of multilateralism when it reins in American power, but much less so when it reins in French and German power--as their reaction to the letter of dissent from eight European countries amply demonstrated. Friedman and Sullivan are hoping to "revive" multilateralism by "encouraging" the world's nations to "do what needs to be done"--in a multilateral, consensus-building way, of course. In other words, they don't really support multilateralism at all; they just wish the world's nations would all "multilaterally" agree with them on how to proceed.
The reason why even multilateralism's supporters, like Friedman and Sullivan, end up being its fair-weather friends is that at multilateralism's heart is a completely absurd premise: that the world's nations form a community, in the same sense that the individual inhabitants of particular locale do. In fact, human communities are made up of people who by natural instinct recognize their own individual helplessness and are inclined to cooperate with their kin--and by extension, with their fellow nationals--for the sake of their own survival. Nations, on the other hand, are largely autonomous units whose populations are instinctively hostile towards distant foreigners, and whose leaders are--each and every one of them--either non-democratic despots motivated solely by the will to power, or else democratically elected leaders sworn to advance their own voters' parochial, selfish interests tirelessly and ruthlessly at every opportunity. To expect such a community of governments to cooperate village-style is simply a foolish fantasy.
None of this implies, of course, that cooperation among nations is impossible. What it does imply, though, is that such cooperation must be based on a clear, explicit and well-understood commonality of interests, not some fond commitment to a higher ideal of global comity. Defense treaty organizations like (the old postwar) NATO, economic organizations like the EU, NAFTA and the WTO, and even arms control treaties, properly verified, can work just fine provided that they are perceived by all the parties involved as mutually beneficial. Where conflicts of interest exist--and they inevitably will, in the ever-shifting world of geopolitical diplomacy--multilateralism breaks down, and simply cannot be repaired. The UN, founded as it is on its false premise of a world community bound by more than mere selfish state interests, has been a horrible failure from day one, and no amount of harsh speeches by American cabinet members, or musical-chairs games with Security Council memberships, can save it.