The answer to your questions resides in yet another question, but back to you: Has France managed to reduce our coalition of nations in Iraq, or has the U.S. grown that coalition into something that makes the UN membership pale in comparison?
Oh, and you also got my "pacificism" wrong. I'm a hawk. Using force is an American strong suit, an option that I favor. For the UN, if merely withdrawing would work to end it overnight, then I'd be in that camp. But it won't.
All that withdrawing the U.S. from the UN would accomplish would be to surrender our UN veto while yielding global diplomacy to the whims of the French and Chinese.
Withdrawing from the UN would be like a pompous CEO quitting his company under the impression that the firm would fold up after he left. Such CEO's are typically dismayed to learn that the firm stumbles on even without their leadership.
Don't be that CEO.
Do we keep feeding this monster? Do we negotiate to save money? Do we even lift a finger when the World Court arrests a US citizen for a 'crime against nature'?