I am with the person that said to take marriage away from the government. Marriage, in and of itself, is a religious ritual, nothing more. The fact that government controls who can get married is a conflict of religious liberties. All person who want to legally bond should be in a civil union, marriage, if a person desires, should be relegated to religious ceremony and the marriages themselves should have no legal binding.
currently, civil unions, in the states which grant them, do NOT confer the same rights and priviledges as marriage, which is discrimination, no matter how you slice it.
Polygamy can be a bit convoluted. However, marital/civil union polygamy can work if there are proper guidelines. If a man wishes to marry two women, he should be able to as long as both women agree to it. However, the catch is, they also become married to each other, and if the man dies, they would still remain married to each other. this would do 2 things. It would cure issues with multiple birthings and custodial battles. Often in 3-way (or more) reltionships, one of the women chooses to stay home with teh children, regardless of who birthed them. The otehrs may work. But each, regardless of staying home or not, is a mother to all teh children and should be legally treated as such. The children should not be divvied up by genetics.
Ok, i ranted a bit, but i think yo9u get my point.