Just as in all societies, marriage has always had to be a matter of law in America. If you don't care if it is legal, then don't make it legal, what is so hard to understand about that?
As far as religion, Islam?, gay churches? Are you guys arguing for polygamy and gay marriage and for the military and federal government to now recognize polygamy?
Legal repercussions of marriage derive from contractual obligations. The link between two human beings is a matter of love and commitment pledged before God.
These are different things, and should be treated as different things. It’s that simple. If you’re married, you should have to specify under what faith, church, our spiritual tradition you are married. It shouldn’t be some generalized government permission slip. It’s identical to calling yourself a citizen. No one is a free floating citizen - every citizen is a citizen of some country, and they are all different relationships and obligations. Same with marriage. If a Hindu priest married two Christians, would they consider themselves married? No. So the religious basis MUST be specified for the word marriage to take place. Not doing so literally allows the government to take the place of the authority of God - which is exactly what it has done, and why there is a “marriage” problem today.
Once a government recognizes gay marriage it has no legal or moral authority to outlaw polygamy. Every legal argument that is raised in support of "gay marriage" will also apply to polygamy.