Richard Epstein recently trotted out an old libertarian talking point after the victory of Proposition 8 in California, effectively banning gay marriage. He suggested that marriage should be a wholly private activity and that there's no need for government involvement. Indeed, for most of American history, marriages were church, not government activities, and there was no need for a marriage license.
Why not go back to those halcyon days of yore and let individuals decide for themselves how to define their marriages?
One reason: divorce.
A couple might have a church or other commitment ceremony to publicly announce their permanent relationship to family and friends, and this can be a non-legal transaction.
But divorce -- the disposition of estate and custody of children, is inextricably a legal activity. And because divorce is a legal action, the marriage necessarily proceeds it is also a legal activity -- or else a person could escape a negative divorce settlement by simply claiming to have never been truly married in the first place. Or, for that matter, than various causes for divorce (e.g. adultery) are inapplicable because fidelity is a not accepted as a requirement for marriage in the opinion of the divorcee.
Like any good Pavlovian libertarian, I start salivating whenever I hear the word "privatize", but I just don't see how the privatization of marriage is feasible.
But what I would like to see is a Constitutional amendment removing marriage from being subject to the Full Faith and Credit Clause of the U.S. Constitution (Article 4, Section 1) so that individual states can define marriage as they like. This way, states that want gay marriage can have it, and those that don't, won't. And homosexuals who want to get married can move to a state that permits it. States that allow gay marriage can be laboratories of democracy, testing whether or not it has positive, negative, or no consequences for society at large.