The gay marriage debate revolves around two very different notions of what marriage is. The traditionalist view sees marriages as having the primary purpose of raising children. The alternative perspective -- adopted by most gay rights advocates -- views marriage as a relationship between two people with emotional and practical functions distinct from reproduction.
Two theories of marriage
The traditionalist perspective dominated ideas of marriage in all societies studied by anthropologists, and throughout recorded history. Marriage as a reproductive union mostly excluded gays whose lack of interest in heterosexual intercourse excluded them from reproduction and regular marriage.
Of course, many societies recognized homosexual unions having other functions such as military apprenticeships among the Spartans, or domestic cooperation and child care amongst Native Americans where a widower married another (transgender) man, or Two-Spirit having both masculine and feminine traits, who then took care of his children.
Marriage can be viewed as an emotional relationship insulated from any practical function, however. This rationale for marriage was introduced to theology in an improbable way by St. Paul who asserted that it is better to marry than to burn. This unusual nod to personal feelings represents marriage is a containment device for dangerously sinful passions that would otherwise destroy the single. It is one facet of the sexual paranoia of the Bible that finds a parallel in immoderate homophobia.
St. Paul was thinking of heterosexuals, of course. And he probably considered marriage as more of a duty to prevent sinful acts than as an individual right to sexual and emotional fulfillment in marriage. Yet, translated into an era of civil rights, his individualistic rationale for matrimony has crystallized as a universal right of all adults to marry analogous to the right to vote.
In those terms, depriving gays of the right to marry gets equated with denying African Americans the right to vote, or to marry people of other ethnic groups. Once the debate is phrased in those terms, the outcome is a foregone conclusion. Very few young people are opposed to gay marriage so electorates of the future will inevitably extend marriage rights to homosexuals. Even some conservative U.S. politicians have begun to follow the tide of public opinion and now accept gay marriage as a civil right.
Rephrasing gay marriage as a civil rights issue is a brilliant public relations move. Yet, it commits a logical error by categorizing marriage as an individual right, something that it never was previously.
A break with history
In the past, heterosexual marriage was a reproductive union. It protected the interests of children and united the families of the bride and groom to this end. Rather than an emotional bond between two people it was a reproductive contract: the wife could expect her husband to support the children in return for which she guaranteed his paternity.
Redefining marriage as a civil right strips it of its defining feature as a reproductive union. This problem is seldom explicitly acknowledged. Yet, it is expressed indirectly in the semantics of the gay marriage debate.
Religious conservatives do not want to permit gay marriage. Yet, many of them are in favor of "civil unions." In other words, gays have a civil right to join civil unions and obtain equal treatment under the law, from employers, and from the Internal Revenue Service. On the other hand, conservatives do not view such unions as equivalent to marriage because they are unions between individuals as opposed to the traditionalist arrangement for raising children.
This distinction may be logically valid but it cannot hold back gay marriage. As far as young people, are concerned, gay marriage is a non issue. This means that electorates of the future will ratify gay marriage in every state. Young Americans are far less religious than older generations as I pointed out in my book Why Atheism Will Replace Religion and they scoff at the sexual paranoia of Biblical tradition.
Politically, it is very difficult to accept civil unions but reject gay marriage. If you have one, as a practical matter, you have the other. A rose by any other name would smell as sweet.
Finally, the distinction between gay civil unions and (full) heterosexual marriage as a vehicle for raising children assumes that gay people do not produce children. Thanks to advances in reproductive technology, that assumption is no longer valid. So gay marriage may arrive as a civil right but soon morph into something closer to a reproductive union.