It sounds great, but in practice it would be tremendously STUPID to give up our UN veto by leaving.
Such a bone-headed move would permit the Tallyrands of the world to outmaneuver the U.S. in global geo-politics; we'd find the international equivilent of union strikes against us as well as treaties that excluded us from certain types of trade...or that singled us out for tariffs.
It would also screw Israel, a nation that depends upon our UN veto to keep Europe, Asia, and the Middle-East from combining to wipe it out politically, economically, and even militarily.
Sometimes "feel good" politics make for bad policy.
If you want to kill the UN, then simply advocate the the U.S. veto *everything* that the UN wants. Grind that place to a halt.
But you can't do that if you've forfeited our veto by leaving.
We leaving will be a permanant veto on the UN itself, and should be accompanied by the creation of a totally new entity, one with principles, transparancy, and accountability. Like Social Security, it needs a true leader to initiate action. A policy of fearing the dark as you seem to favor never gets anyone anywhere.
On the other hand, I'm not so certain that the US can veto abosoutely everything.