Gay marriage is a topic in the United States that will split many reasonable people. Being Australian, in a country that doesn't even accept civil unions, maybe I'm not the best person to talk on the matter. But I will.
I don't passionately believe in gay marriage on the basis that I believe in equal rights (although I'm favorable to that argument.) Instead I believe in gay marriage on the basis that the state marries people, and the state should never discriminate. If you seriously believe that marriage is between a man and a woman on religious grounds, you should also believe that the state shouldn't be allowed to marry people,
Of course you'll never here that from the anti-gay marriage folks.
If the religious ideal of marriage is based on a man and woman, then there should be no state based marriages, period. If we allow the state to marry people, as any good libertarian should, then the sexuality of the pair should be irrelevant.
As someone who has been in a heterosexual marriage (be it not much longer) I've never seen how two blokes getting married threatens my (soon to be ex) marriage. Indeed, if two blokes or two women are happily married and don't get divorced, all the better for them.
If you disagree, leave a comment. But if you're to the right, explain how the concept of small government fits with interference in marriage. Libertarianism means less Government, which to me means supporting gay marriage on the basis that Government shouldn't interfere.