Backwards as I think the U.S. government is on many issues, the UN is all that if not worse. One need only look at the goings-on during many UN "peacekeeping" operations to see that.
While there's no solution to the homosexual marriage issue that's going to please everyone, I think one major step would be to decouple (no pun intended) religious marriage from civil marriage. Despite America's much-vaunted (and, by historical standards, largely successful) policy of separating Church and State, we still see a marriage performed in a church (to most Americans, read "Christian church or Jewish synagogue") as a one-size-fits-all act of spiritual union AND civil union. Nice and traditional...except the U.S. Constitution actually precludes government from involving itself in religious matters, or granting special privileges pertaining to the rites of a specific religion but not others.
What we really need is for the government to wake up one day and say:
"As of today, we're no longer in the business of defining or performing or certifying marriage. What we will allow and facilitate, between any two consenting adults, are civil unions. A civil union grants property rights, parental rights, and power of attorney in the unfortunate event of the incapacity of one partner. That's it. We don't claim to be acting as an agent of God, Lucifer, Jehovah, Allah, Buddha, Xenu, Zeus, or the Flying Spaghetti Monster. It's just legal paperwork certifying a union between two individuals.
"If you want a ceremony invoking or involving the powers of divinities or other such agents, like "marriage under the Lord" or consecrating your baby to galactic overlords or handfasting on the summer solstice under the good graces of the Earth Goddess, or what-have-you, that's not our department. We're the State, not Church. You are free to perform or undergo whatever such ceremony you wish on your own time. It will have no legal significance (unless you choose to enter into a contract with one another above and beyond the civil union, like a prenup), but it will have whatever spiritual significance floats your boat. You are free to specify the circumstances under which the cermony may be performed. If you want it to only be allowed between a male and female, hey, there's this nifty First Amendment thingie that keeps us out of the loop. But you can't deny civil unions to homosexual couples, because just as that First Amendment keeps us out of your business, it likewise keeps you out of ours. Have a nice day."