OK, since no one (except Stephen Milliken) is excited about monism, here are some theses about gay marriage:
1. Gay marriage really is the redefinition of marriage to make it gender neutral. It is not simply the granting of "equal access" to an institution whose meaning remains the same.
2. However, given the shifts that have taken place in our cultural understanding of marriage, such a redefinition makes sense. That is to say, we have privatized the concept of marriage and defined it in terms of the desires and needs of individuals, while questioning traditional "essentialist" ideas about gender. Hence, it no longer makes sense to many people to define marriage in gendered terms.
3. The trend toward erasing gender differentiation is the root of gay marriage.
4. Gender differentiation is a natural given of the human condition and thus should not be erased, but the way it has been expressed historically is always shaped by sin, and so the recent reaction to gender norms is both a needed correction and itself the source of a new set of sinful "cultural constructions."
5. The concept of "homosexuality" as an intrinsic part of some people's identity, defining who they are, is probably best seen as a modern invention, parallel with the concept of race, and shaped by particular kinds of gender norms in the modern West. If homosexuality is to be seen as an intrinsic part of a person's identity, then it ought to be affirmed as a good part of God's creation. But it is not clear that it ought to be seen in these terms, given its culturally constructed nature.
6. Opposition to gay marriage rests on the belief that gay men ought to be treated just like straight men in terms of marriage law, and gay women like straight women. In that sense it is radically different from opposition to racial intermarriage to which it is often compared. However, it's true that this results in gay couples being treated differently from straight couples.
7. Whatever one's position on gay marriage per se, it is abominable that same-sex couples are not able to have practical benefits such as visitation rights and joint tax returns. This really is a question of simple justice, and as long as these basic legal benefits are only extended to married couples, civil marriage for same-sex couples is indeed a basic mandate of justice.
8. Civil unions, the briefly considered and swiftly abandoned compromise, are not "separate but equal" if they are made available to everyone. Marriage, of course, already was available to every adult as an individual, but not to every couple (that is, gay people could marry, but they had to marry members of the opposite sex. While this may seem to be a "useless" right, it is nonetheless exactly the same right that straight people have.) Hence, there would be no inequality in retaining the word "marriage" for opposite-sex unions, while granting identical practical rights to any two (or possibly more) adults who wished to enter into a civil union. (Of course, this would not necessarily imply a sexual relationship, which simply isn't the business of the state one way or the other.) However, given the present state of affairs, the best approach may be for the state to drop the word "marriage" altogether.
9. Contrary to common belief, the specifically Christian arguments for gay marriage (rooted in the overturning of gender norms in Jesus) are much stronger than the secular arguments, which are generally question-begging (inasmuch as they assume the validity of broader cultural shifts which genuine conservatives wish to contest in the first place).
10. Faithful, loving relationships between equals are always, in themselves, good. Hence, the pictures of happy couples celebrating yesterday ought to be cause of rejoicing to all decent people, whether or not we agree that "marriage" is the right word to use for those unions.