Notice that the below commercial in support of excluding gays from civil marriages in Minnesota actually offers no direct argumentative supports for the position at all.
Watch:
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In the intellectually bankrupt culture surrounding the anti-gay marriage movement, it’s taken to be acceptable to substitute oppositional reasons with nice music and calm tones of voice. Concerns expressed in the commercial are at the periphery of the issue—such as worries about process. One person, for example, wants elections, not judges, deciding. That’s an argument for democracy, not against gay marriage. Another is nostalgic for how things were when he grew up. Again, this in not really an argument; it’s a complaint. Still another says heterosexual marriage is just the way it is, and should stay that way. This restates the anti-gay marriage position, but doesn’t provide any additional support for it.
Weak, peripheral (or completely absent) reasons for opposing gay marriage are why the anti-gay marriage movement is likely to lose, and deserves to lose. If it doesn’t lose at the ballot box, it must lose in court. Judges want arguments.
So, what work is really being accomplished by this ad? It soothes the conscience of those inclined to vote against gay equality; it assures them that they’re nice people and aren’t bigots. And it suggests to the viewer that there is simple strength in numbers. This is true. Intellectually, you can be asleep and still win.
But what are the actual arguments against gay marriage again?
Prometheus Unbound 
Girgis, George, & Anderson, in the Harvard Journal of Law and Public Policy, have written an extremely cogent paper that defends the traditional notion of marriage as union of husband and wife, and addresses some common objections that supporters of same sex marriage bring up. I highly recommend it, as it contains the clearest objections to same sex marriage, without any reference towards religion (other than the inevitable threat towards religious freedom that it presents). It’s a fairly lengthy paper, but very comprehensive. You can find it here: http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1722155
David,
Thanks for the link. I’ll have a look. But why is gay marriage an “inevitable threat towards religious freedom”? In what way is it a zero sum game?
If anything, the religious freedom question goes the other way: there are minority religious congregations willing to marry gay people, but they are not being treated equally by the state.
—Santi
It doesn’t necessarily need to be a zero sum game if there was a strong conscience clause that would protect churches, mosques, and synagogues from law suits or civil penalties for refusing to allow same sex marriages in their facilities, or for individuals to refuse to participate. But once you have same-sex marriage enforced by the state, it is inevitable that people would seek to push the issue further, particularly when objection to same-sex marriage is consistently framed as being nothing more than mean-spirited bigotry. In England, for example, there is an MP who wants to ban churches from having marriages unless they also provide for same-sex couples (http://www.agoracosmopolitan.com/news/religion/2011/10/04/951.html). It could be argued that England does not have the same level of protection towards religious freedom that we have in the States, but still there is probably much that state and federal lawmakers could do to make life extremely difficult for religious organizations that do not support same sex marriage, such as by imposing fines or removing tax exemption.