There are two competing approaches to gay marriage emerging from state legislatures and courts. First, Vermont is trying civil unions, essentially a contract approach to marriage. Allowing civil contracts as a practical substitute for marriage appears quite workable, and avoids the conservative trigger word "marriage." If the state will enforce a civil union contract, it gives most gays what they seem to want while still reserving traditional marriage for "as between a man and a woman" relationships.
Alternatively, Massachusetts is apparently opening the doors to full-fledged marriage for gays. As I see it, traditional marriage confers a status rather than creating a contract. Traditional marriage is not a contract. Status changes the legal position of the parties beyond merely being subject to the terms of a contract.
For example, minors are subject to certain limitations simply because of their status: besides contracting limitations, they cannot vote, must attend school, etc. (but they can often marry if over 16 with parental permission, despite not being able to form contracts!). That's not a contract arrangement, just a status the law applies to minors that affects their legal standing, rights, and obligations.
Felons are subject to certain limitations. It's a status; not a contractual relationship.
Go back two hundred years: slave was a status category. "Chattel" might appear to be a designation that made some people subject to property laws, but in fact they were humans with a status label, not real chattels. You can't manumit a horse or a chair and make them free persons with legal rights.
Likewise, "married person" is a status, not the consequence of a contractual relationship. A married person gets special tax rates (perhaps better, perhaps worse), gets certain inheritance benefits, may qualify for special immigration or citizenship rights from the government, gets rights as to custody of children and presumption of parentage, etc. The status comes after a voluntary ceremony or visit to the local magistrate, but it's hardly a contract negotiation in either form or substance.
There is no reason the state cannot authorize civil unions (synthetic marriage providing by contract many of the perks or mutual obligations that come with the "married person status") while the parties remain plain vanilla single persons legally, not becoming "married persons." Of course, persons entering into marriage may enter into contemporaneous contracts, prenups, but that's optional and distinct. Historically, consider common law marriage, where states seemed willing to recognize the couple as "married persons" despite the existence of neither an express contract nor a marriage ceremony.
Now here's the kicker that I have heard no one discuss thus far. A well designed civil union contract might offer some benefits that traditional "status marriage" does not. If so, some hetero couples would likely be interested in civil union as opposed to traditional marriage, and they should not be denied access to civil unions--that would raise an equal protection problem. So hetero couples might consider the choice between civil union (contract marriage) and traditional marriage (status marriage). How would simply increasing the options available to all parties make anyone worse off? Seems Pareto-optimal to me, and by not forcing the traditional "marriage" label on civil unions it would defuse much of the conservative opposition.
So if the Massachuesetts courts would just stay out of the process, the Vermont civil union approach could evolve into a workable solution without igniting a new phase of the American culture war.
Note: This approach developed as part of a discussion with my friend Tim after his discussion of a similar topic.