Phobia.

Opposition to gay marriage makes even less sense than most social-conservative policies. The arguments dreamed up in its defence are particularly pitiful. But it's my belief that we don't even need to answer those arguments directly. Sure, we can point out that the existence of gay married couples doesn't in any way degrade existing straight marriages, and if a straight couple feels that it does then it's the fault of their own bigotry; we can point to studies showing that children aren't any worse off, socially or psychologically, with gay parents, and to similar rates of divorce among straight and gay couples in places where it's already legalised.

The first reason is that in this area, the law is relatively powerless. Civil unions confer many of the major benefits of marriage and are a definite step in the right direction; if you're savvy enough, or know someone who is, you can draw up contracts to cover most of the rest of it. Yes, it's not neat, and it's probably not cheap, but it's doable. Furthermore, the only people who talk about civil unions are the people whose business is the law. No young Romeo is about to fall to his knees and cry "Julian, my darling. Will you civilly unite with me?" (Linked, an explanation far better and conciser than I could write.) You might not be "legally married", but if you've got your own priorities straight, you'll be as married as the rest of us where it really counts.

Second reason: We throw around words like homophobic to label people who oppose homosexuality. Why -phobic? We have racism, sexism, speciesism, but here we attach a label that in most cases describes either relatively benign psychological conditions (acrophobic, claustrophobic) or mundane scientific phenomena (oleophobic, hydrophobic). We don't mean it that way, but it lends an aura of acceptability, inevitability to what's really just simple bigotry. "I can't help it; I have a phobia."

But the reality is that it doesn't matter if the Marriage Act is homophobic. No really, it doesn't. We don't need to convince people that homophobia is wrong before we convince them to change it. We can argue against it from a principle that a lot more people accept: that sexism is wrong. It doesn't matter if it's homophobic, because it is also sexist and that should be enough to prove that it's wrong. To wit: subject of course to her consent, I could theoretically marry just about any woman I chose. But I couldn't marry a man no matter how well I knew him or how much I loved him — not because I or he was gay, but because we were both male. Sure, the law exists for homophobic reasons, but it can be torn down on a gender equality basis.

By the way, to any couples planning to get married in Australia, if you're told your celebrant has to read the part of the Marriage Act that defines it as being only between a man and a woman or else your marriage will be invalid, pay attention. This part came as a bit of an unpleasant surprise as we were planning our wedding. More recently, I've looked into the actual Marriage Act. Nobody's going to come along and tell you you aren't "really married", or take away your legal rights. One part of the Act does indeed list those particular words as a requirement to be read at the ceremony, but a couple of sections later is the part that talks about grounds on which a marriage should be considered invalid and failure to have those words read is specifically excluded. I'm no lawyer, so don't take my word as gospel: but look into it for yourself, and work something out with your celebrant, if those words make you as uncomfortable as they make me.