A response to my post. I think Reihan's point is that social conservatism resists change and that therefore extending civil marriage rights to gay couples is inherently liberal. The reform corresponds with the evolution of civil marriage away from procreation and toward companionship - and social conservatives worry about such change. In that sense, I don't disagree with Reihan's point. The most coherent conservative objection to same-sex marriage is simply resistance to any tampering with a vital social institution. I respect that position; it's certainly devoid of bigotry; and, as longtime readers know, I'm happy to let this evolution proceed state by state for Hayekian reasons.
I suppose marriage equality is socially liberal in as much as it tries to defend and integrate a previously despised minority. But it is socially conservative in its attempt to envelop that minority in the traditions and responsibilities of family life. In this, it is exactly the same as welfare reform: ending a disincentive to family life among a minority that needs more social stability. I have to say that having finally begun to live a married life, all my previous intuitions about its integrating impact have been borne out more profoundly than I ever imagined.
If you can make the leap to seeing gay people as the equal of straight people, then encouraging their marriages to one another is arguably one of the most socially conservative measures now subject to national debate. That's why it remains so saddening that so many social conservatives still regard it as definitionally anathema. I don't think it's a leap to believe that homophobia or fundamentalism are the critical stumbling blocks. Or that they are the real reasons for the resistance.