As more gay couples come out and say "We're here. We're queer. Get used to it," and don't stay in the closet, and when society sees that gays are and will always be in long-term loving relationships on par with marriage, laws against gay marriage will come crashing down.

I enjoyed this thread for the different perspectives.  As I see it, equality under the law is a basic principle of legal philosophy that should make it illegal for the state to discriminate between straight and gay.  And the constitution, properly interpreted, should take care of that.  But, I'd like to point out that any license, whether one is getting a license to operate a business, or a license to get married should be seen as a prohibition.  The state is saying, "Meet the terms of this license, as decreed, or you will prohibited from this entire class of actions."

The state only has the following fundamental power: To direct the use of force, and its two derivatives: to prohibit and to confiscate (both of which presuppose the capacity to direct force, or to threaten to direct force).  That's it.  Prohibit or confiscate.  So when a state issues a license what it is really doing is threatening that it will use force against anyone who engages in the actions defined by the terms of the license without meeting the specified terms.  It is a prohibition (backed by the threat of force). 

The terms of the license are whatever the state says.  Maybe you have to be a certain age, and/or pay a fee, and/or get a blood-test, and/or as once was the case be of the same race, or are of opposite genders.

A license is always a case of the state threatening to use force against those who have violated no one's rights.

The state has a proper function in providing a mechanism for resolving civil disputes.  We have a rich body of contract law that plays an important part in enabling a rational method for resolving many disputes.  There can be specialized terms in contract law for different kinds of contracts but none of that should go to the point of telling individuals what they can or cannot do so long as they do not engage in the initiation of force, threat to initiate force, steal or commit fraud.

When the state creates license laws, they are not simply enabling contracts or engaging in contract resolution - such as any law relating to civil unions.  No, they are prohibiting some people from entering into a contract.

The business of putting the state in charge of the definition of marriage is both offensive and dangerous and it is also a subterfuge.  A romantic relationship (regardless of its economic impacts or effects on child custody or inheritance) is between the parties and not the government.  We should be offended that the state intrudes to tell us what romantic relationships we can have.  If some man decides to marry his pet duck, I won't go to the wedding and will steer clear of him, but if he can find someone to marry them that is his right (although it might be a case of cruelty to animals).  Would I call that a "marriage"?  I would call it a neurotic or even psychotic kind of marriage.  Those who try to mix up the definition of a word with the state's power to prohibit are falling for a kind of intellectual bait and switch.  Like those who focus on a license as 'giving' something to someone, instead of focusing on how it is actually a method for prohibiting actions to others.