The Rawlsian Case against SSM?

Matthew O'Brien has posted a new paper, Why Liberal Neutrality Prohibits Same-Sex Marriage: Rawls, Political Liberalism, and the Family.  If you (like me) have never considered Rawls to be a potential linchpin in the case against SSM, you should probably check out the paper.  Here's the abstract:

John Rawls’s political liberalism and its ideal of public reason are tremendously influential in contemporary political philosophy and in constitutional law as well. Many liberals are Rawlsians of one stripe or another. This is problematic, because most liberals also support the redefinition of civil marriage to include same-sex unions, and as I show, Rawls’s political liberalism actually prohibits same-sex marriage. Recently in Perry v. Schwarzenegger, however, California’s northern federal district court reinterpreted the traditional rational basis review in terms of liberal neutrality akin to Rawls’s ideal of “public reason,” and overturned Proposition 8 and established same-sex marriage. (This reinterpretation was amplified in the 9th Circuit Court’s decision upholding the district court on appeal in Perry v. Brown). But on its own grounds Perry should have drawn the opposite conclusion. This is because all the available arguments for recognizing same-sex unions as civil marriages stem from controversial comprehensive doctrines about the good, and this violates the ideal of public reason; yet there remains a publicly reasonable argument for traditional marriage, which I sketch here. In the course of my argument I develop Rawls’s politically liberal account of the family and defend it against objections, discussing its implications for political theory and constitutional law.