The argument for matrimony goes along these lines: marriage is a fundamental human right that encourages the establishment of stable partnerships and families. The state has an interest in recognizing these unions as a stabilizing economic and social force, conducive to "the pursuit of happiness" enshrined in one of our founding documents. Therefore it extends a host of legal benefits to married couples as a function of the idea that each person should be able to designate another genetically unrelated human being as a member of his or her family.
Gays agree, citing additionally the social status of marriage that is denied us in even the most comprehensive domestic partnership/civil union legislation. As a class of people who is defined by an attribute beyond our control -- sexual orientation -- we are in a protected class that should not be denied equal protection under the law. There is no more justification to outlawing same-sex marriage then to outlawing interracial marriage--but the consequences of doing so are substantial. On the federal level alone, the unmarried couple loses out on 1100 benefits allowable only to married couples.
Gays are right of course: if straight people can get married, then there is no reason we shouldn't be able get married. But in our haste to join up in this system of marital apartheid, we have ignored some basic truths that will still apply to all people regardless if all unrelated consenting adults can still get married.
There are few human beings who don't want love and companionship, in fact, the vast majority of us spend a considerable portion of our youth looking for it. But half of all persons who think they have found "the right one" find out they have made a mistake and get divorced; the rate for second marriages is even worse. By the time one reaches middle age, the statistics are clear: one is as likely to be single (via divorce or never having been married at all ) as one is to be in a first and only marriage.
We are called upon by the state, by the culture, by vows repeated endlessly: "not to enter into this union lightly." At the writing of the Constitution, divorce was an option in only rare and extraordinary cases. If it is in the societal interest to encourage marriage, it has always also been in the societal interest to discourage short or unhappy marriages that result in spousal violence or unwanted children who end up abused or abandoned to foster care. Society often pays the price when marriage doesn't work.
So there is literally complete agreement on both sides of the spectrum that no marriage should proceed without the basis of profound and mutual love and respect, or at the very least, a sincere effort to determine a level of compatibility that feels sustainable to both parties over the long-term. We pretty much all try to find someone who fits these parameters. Some of us succeed, some of us succeed for a time, some of us never succeed once. The bottom line is: even if the day comes where every one can get married, not everyone will actually be able to get married.
So why should those fortunate enough to be find "that special someone," (some several times over - I'm looking at you, Newt) be granted 1100 other special rights not available to those of us not fortunate enough? Why should all of the Americans -- gay or straight-- who have chosen support systems that involve a complex network of of close friends and family members, be deprived of the right to assign similar benefits that are available to married folk to any of these individuals? What right does the state have to place more value on marital relationships than on non-marital relationships?
This transcends the gay/straight divide. Even with the advent of gay marriage, these rights will not be available to those, who by choice, circumstance or both, don't find a partner who is willing to commit for life. Intent is not determinative here. Luck counts - a lot. Being in the right place at the right time to meet the right person cannot be decided. Many Americans who suffer from dysfunction or disability or geographical inaccessibility are much less likely to find themselves in the marriage pool. Their "right" to marriage will exist on paper, but will remain, in reality, elusive.
A celebration of the love of two people should always be permitted and will always be desired. No one is suggesting the suppression of that aspect of marriage. But legal recognition by the state should be exclusively under a different set of "Plus One" laws. This would mean everybody would have the right to assign the same set of legal benefits available in marriage to anyone they know, and not necessarily to the same person. For example, in this overloaded example, I might sponsor a friend who wants to immigrate from Canada, while giving my roommate my health insurance. My boyfriend might want to give me his Social Security survivor benefits, while giving his airline buddy passes to his sister to visit her daughter away at college. A close girlfriend and I could assign co-parental adoption rights to each other because we decided to raise a child together.
I could also choose one person to have all these rights -- a man or a woman whom I love or with whom I am just close friends. Our agreement could be renewed every few years or lapse, recognizing that relationships change over time and the law should reflect this natural fluidity of the human condition.
I don't have much illusion that there is any chance of some version of GROMA (Getting Rid of Marriage Altogether) being proposed or passed any time soon.. The cultural attachment to heteronormative ideas of marriage is so strong that my gay brethren have signed up to sign on to it with a vengeance. It will probably take the waves of inevitable gay divorces for the newly-left-behind to feel solidarity with those who never got on the marriage train in the first place. Together with the single-by-choice and circumstance, the divorced, the widowed and the tentative, gay and straight together, we shall confront the system that rewards the lucky in love with first-class citizenship and leaves the rest of us to pursue our happiness with fewer rights and resources.