Now imagine a bureaucracy run by and accountable to all the national government bureaucracies in the world! And remember that the ones most HN readers live under are, despite our whining, the most efficient and least corrupt in the world - the others are often far worse.
That's the UN. If you are going to have an association of the world's governments, I think that's the way it's going to be.
Like democracy, it's horrible but better than all the alternatives. It's primary purpose, IIRC, is to prevent international war (i.e., wars between nations, as opposed to civil wars). After all the war of human history, after WWI and WWII occurring within a 31 year period (think of that: that's like 1985 until today!), international war has almost been put to an end. It's now a major exception when it happens, and that fact is really a miracle.
They also achieve many other very important things, though expensively and slowly.
Remember that the UN is no fuzzy-minded idealist's fantasy. It was built by the survivors of WWII and WWI, while the ashes were still smoldering. Those people knew far more of war and the realities of man's inhumanity than we can imagine.