Lost in the acrimony is the one thing both sides agree on: that government should define and provide civil marriage. Yet this is arguably the source of the trouble.
From a policy perspective, legal marriage is a collection of contractual arrangements between the government, the marrying couple, and their children (if any). In particular, marriage establishes default rules about inheritance, division of common property, and guardianship of children. And civil marriage bundles all these contractual rights and responsibilities.
Governments probably should define and enforce default rules about each component of the marriage contract, such as those about who is the legal parent of a minor child.
Governments can do this, however, without defining or “supplying” marriage. Indeed, governments already do so. If an unmarried woman has a child, government rules determine this mother’s rights and responsibilities with respect to that child, as well as those of the biological father. Likewise, government rules already exist regarding communal property and inheritances for people who are not married.
By exiting the marriage business, governments would avoid any necessity of taking a stand on gay marriage. This would calm the debate and polarization over this issue. Couples that wanted the particular bundle of contracts included in civil marriage could arrange for this through private contracts. Paradoxically, government exit from the marriage business might strengthen religious marriage, precisely the goal of many gay marriage opponents.
The approach outlined here is, without question, unlikely to occur. But it still provides a useful framework for thinking about gay marriage. Viewed from the “contracting” perspective, the main argument for civil marriage would be that this particular bundle helps vulnerable groups, like children. This claim does not seem particularly convincing. If it is, however, it presumably applies to children of same-sex couples and opposite-sex couples alike. Thus, the contracting approach says that if governments do provide marriage, they should include gay marriage.
Would this then mean governments had to provide civil marriage for polygamous relations? Not necessarily. Governments might reasonably decline to provide polygamous marriage simply because such contracts could easily become hopelessly complicated and difficult to enforce.