For what gay marriage is to homosexuality, group marriage is to bisexuality.
I've never heard it phrased exactly that way, and yet it rings true. The best part of the Dutch "cohabitation contracts," to me: it's a private contract. The problem is that many of the anti gay-marriage laws and amendments on the books or on their way there would void this sort of private, contractual arrangement--or even make it a crime to attempt to create such a contract.
Is this a "slippery slope" or social progress? I guess it depends upon which "side of the aisle" you sit. I, for one, would love to see the aisles married folks walk be made wide accessible for parties of three, four, or more. Will many require such accomodation? No, of course not. What possible harm could it cause to make room in our society for those few who do?