Re: Polygamy and yes civil unions! (dun dun dun)
there are three, or more, person contracts made all of the time. they are made then multiple people own a company, or anything like a house, car, rights to music or basically any other thing. You can make a contract for joint ownership of just about anything you want.
Divorce is hard on children no matter what kind of relationship their parents had.
And i think that you are underestimating the complexity of the current system. there are many cases where more than two people are trying to get custody of a child, usually it involves the parents being unfit to raise the children but still, a parent vs. parent vs. grand mother vs. state custody vs. step father or W/E can happen.
The strange thing is that there are polygamist couples out there (not very many) some are because of religious beliefs and some aren't, but the point is that they are out there and they aren't "illegal" because the government doesn't stop people from living with/having babies with/"marrying"(not in a legal sense) more than 1 person at a time, just like they don't make homosexual relationships illegal, they just don't give them legal marriage status.
Plus do you really think that it being really complicated is good reason to make it illegal? If every thing that was really complex in the legal system was made illegal no one would have to pay taxes lol. Something being really complicated shouldn't decide whether or not it is legally recognized. I assure you that there are many things more complex than a three way legal battle for custody of (a) child(ren).
Plus are you listening to what you are saying? that point amounts to something like "your love for each other is too legally complex, so it shouldn't be legally recognized."