Within the debate on same-sex marriage in the United States we have countless times heard the refrain that traditionalists are not homophobic, but rather wish the preserve the sanctity of the religious institution of marriage. This argument, in fact, was the main crux of the defense of Proposition 8 when it was debated in California in 2010. Now, as state after state considers its laws in light of the recent rulings that have severely weakened DOMA, one anticipates this argument to continue to come up on the state level. This argument is legally important, as it allows one to separate the preservation of the sanctity of marriage from the animus associated with homophobia. As the Proposition 8 and Supreme Court trials demonstrated, animus can not be used as a justification for the support of a law.
There is a dirty conceit that conservatives would do well to admit though: such a separation is simply an argument of convenience. To show this, let's begin by assuming that one can separate homophobia from a religious justification for traditional marriage. If this were true, one might expect that in states where traditional marriage was outlawed, other laws providing rights to gay and lesbian citizens would find more favor among local governments and voters. Yet, what we observe is the opposite: in states where gay marriage is forbidden, there has been substantial opposition to many other rights as well.
Simplifying a bit, the types of rights that gay and lesbian people have sought usually keep to the following trajectory. First, the right to consensual relations was sought. Second, non-discrimination in education, housing, or the workplace was sought. Third, some type of legal recognition (domestic partnership or civil union) for one's relationship was sought. Finally, the right to marry was sought. In those same states where same-sex marriage is outlawed and where its opponents argue that their position isn't driven by animus, one finds resistance to non-discrimination ordinances or even to consensual relations among same-sex partners (as in much of the southern US).
If it were just about the institution of marriage, and nothing else, then what on earth is the motivation for resisting the passage of all the other possible rights for gay and lesbian people? I don't know the conservative response to this question, but I would like to hear some rational argument if it exists. The notion that one can separate upholding the religious institution of marriage from a motivation from animus may sound good in theory, but actual practice shows us otherwise. And as a true empiricist (and positivist), I trust my observations.
If I were to call a spade a spade, I would say the separation argument is simply an attempt to save face in social circles in light of broader social acceptance of gay people and their relationships. After all, one can "hate the wedding but not the wedd-er" and still be in the in-crowd. Taken as such though, this sounds more like a social coping mechanism for someone uncomfortable with gay people than a legal argument used to oppose same-sex marriage.