Larison makes his case against marriage equality:
When endorsing a change, particularly one this radical, a conservative would need to show not only that it does not do harm to the institution in question but also that it actually reinforces and reinvigorates the institution. Whether or not “gay marriage” harms the institution of marriage, it certainly does not strengthen it. It is therefore undesirable because it is unnecessary to the preservation of the relevant institution, and so the appropriate conservative view is to leave well enough alone.
"My Big Fat Straight Wedding" argues the opposite. I think allowing gay couples to marry does strengthen the institution, because it ensures that everyone in a family has access to the same civil rites and rights, and so the heterosexual marriages are as affirmed as effectively as the gay ones. (It is not my experience that the straight siblings and families of gay people feel their marriages affirmed by excluding some of their own.) By removing the incentive for gay people to enter into false straight marriages, which often end in divorce or collapse, wrecked childhoods and betrayed spouses, heterosexual marriage is also strengthened. And the practical alternative to marriage equality - civil unions for straights and gays - presents a marriage-lite option for everyone that clearly does threaten traditional marriage in a way that gay marriage never could.
Serious conservatives understand that these are the three practical options on modern America: including everyone in civil marriage; creating a two-tiered system of civil marriage and then lesser civil unions for straights and gays; or simply resisting any change and using the government and law to perpetuate the stigmatization of homosexuality. If those three are the choices, my view is that the first is easily the most authentically conservative. I suspect that the impact on those states that now allow such inclusion will prove it in due course.