"just a decriminalization of polygamy would be sufficient."
yeah right. Then you'll want to marry your siblings, aunts and uncles, etc.
Are you trying to give a new meaning to "relativism"?
Polygamy is certainly not the same as incest. And if both the man and the women want to live such a lifestyle, why the hell should they go to jail for that? They're not harming anyone, so they should be free to practice polygamy.
After all, America is all about personal freedom, or at least it was when our forefathers wrote the Constitution.