When I was young, and ferocious feminists roamed the earth, it was a widely held view that marriage mainly benefited the state. Why should committed co-habiting couples need official sanction? Of course, people kept on getting married nonetheless (including formerly ferocious feminists). Except when they couldn't.
It is true that marriage serves the common good. A sizable marriage penalty is written into the tax code; rich and poor, working married couples pay more in taxes than they would if single. Married couples are more likely to fill caretaking roles for each other, saving government money in social benefits for the sick or disabled. And married parents have the legal responsibility to support their children, making the children less likely to become wards of the state.
The government does shell out Social Security survivorship benefits to married people and not to co-habiting couples, no matter how long they have been together. But the cost is small compared to the economic value marriage generates.
Leaving aside all questions of fairness, marriage between committed couples, no matter what their sexual persuasion, should be encouraged simply on the basis of the bottom line. Yet there is heated opposition to gay marriage, much of it on religious grounds.
So why not take the state out of the marriage business altogether? Straight or gay, all couples would enter into the same kind of civil unions now proposed for gay couples. These would be carried out by the government, and would confer the same rights, benefits, and obligations as marriage now does. Couples wishing to enter into a marriage sanctified by a church could do so as a private, supplemental matter. And there would be no need for one group to impose its beliefs on anyone else.
There would be another benefit as well. It would take the divisive issue of gay marriage off the table in the coming presidential election. I find it painful to watch candidates tie themselves in knots over this one, and, frankly, we as a country have more pressing things to worry about.