If society (and government) does not hold firm on the basis of all human history and morality, it the reason for marriage is not to create and raise the next generation, but simply to certify your biding to who (what?) you "Love"....then there is absolutely no historical, moral, or legal basis to forbid polygamy or polyandry....or for that matter someone "marrying" his/her dog, cat, horse, or even house or car. God (or biology for you atheists) created the sexes who together create new life and nourish the next generation. Marriage was the state establishing and certifying the "Good" of that purpose. Now, the only "Good" is do what feels good..to you.
America is gone....what is left may take a long time falling, but fall it will and must. I won't be here to see it (probably). Neither will most of you. But the next generation(what's left of it) may.
The 22nd Century (2100->) will probably be the "Chinese Century", if even they are left to contest for the title. Perhaps it will be the "Muslim Century", with the 12th Imam creating the world-wide Caliphate. It certainy will NOT be the 3rd American Century. We are now beyond even having a 2nd American Centry.