Most people will agree that marriage in the US is very much a religious institution. Many faiths and denominations have such things in their holy books, although some of them (Deuteronomy 25:5-6) are now viewed as quaint or obsolete - like a man marrying his dead brother's wife (Yibbum).
It is the religious nature of the institution of marriage that fans the flames against gay "marriage" in so many people - it "profanes" the institution in their view. Well, you can't profane something that isn't sacred.
Then we have the government, and the Constitution. Let's look at Amendment 1:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.So, in essence, Congress can't make laws about religion, or religious institutions, or to prevent religious practices (that don't endanger others.)
Well crap! Having government established criteria for marriage (an ancient religious institution) runs right smack against the First Amendment!! The government has no business regulating marriage, or giving benefits for marriage, or rights only to married couples. None. Marriage is religious.
But what about inheritance, survivors pensions, visiting rights in hospitals, married filing joint, and all of that which is currently attached to marriage?
It needs to go. All of it. No more marriage licenses. None. Marriages can only be performed by a religious authority, who sets their own faith-based criteria. No civil benefits should accrue from such a ceremony.
Congress shall make no law respecting an establishment of religion: marriage is such an establishment. Return marriage to the churches, synagogues and mosques where it belongs.
But the rights and priviledges formerly accorded to "married" couples?
Well, they belong as a civil matters, not religious. Inheritance, childrearing, hospital visitation, final decisions, taxpayer status - all of those are civil matters, not religious ones. They require their own civil statute, and civil institution. They are rights and responsibilities gained from a civil contract, currently tied to the otherwise religious institution of marriage.
Break the link between the civil and the religious. Makes all unions/legal pairings/whatever be civil unions. Hetero or homo, it doesn't matter. The civil part is a civil union. Go before a justice of the peace, both declare your intent to enter into a contract of union in front of witnesses, and the contract is legally recognized.
Since it's civil, it can be regulated for the sake of the public health (brother/sister or father/daughter unions, for example), but otherwise it falls under the equal protection clauses. If the couple wants a religious marriage too, then they can have one, in the religion of their choice.
The justice of the peace could even deputize the religious officiant to perform both the marriage and the recognition of civil contract at the same time. That's really what we have now, but it's all buried under the religious institution of marriage.
It takes the government completely out of the institution of marriage. It maintains the civil contract part that is the government's bailiwick, and gives marriage back to religion.
Oh, and divorce? A dissolution of the civil contract - only. If you want to marry again in your church, you have to dissolve the marriage according to their rules.
Furthermore, if a religion believed in polygamy, they could marry groups. But civil law would govern who had the civil union contract, and thus the tax benefits and such.