Catholics don't get to define my marriage — even if I am heterosexual. From Pharyngula's blog

http://scienceblogs.com/pharyngula/2010/08/catholics_dont_get_to_define_m.php
Category: Equality

Some Catholic site is giving advice on how to field questions from Leftists about homosexuality. After all, those danged lefties keep bringing up issues of equality and civil rights when gay marriage comes up, and it's awfully hard to talk about restricting gay rights without sounding like a bigot or homophobe, so you've got to have a different set of talking points you can switch to whenever talk about equality and fairness and those other non-Catholic doctrines are brought up. So they've come up with five different tactics Catholic bigots can use to divert attention from their bigotry. They hope. Mainly, though, it diverts attention to the fact that they use really, really bad arguments. Here are the five, reworded from their misleading rhetoric to a blunter description of what they propose.

1.

Obfuscate about rights. Redefine rights any old way you want to, endorse equal rights for everyone, but then claim marriage isn't a right because there are restrictions (can't marry your sister, there's an age of consent, you have to pay a fee to get a marriage license), so it's OK to add one more restriction. Never mind that by this reasoning the old miscegenation laws are perfectly valid, and don't really deny anyone a right.
2.

Point out that heterosexuals have damaged marriage. How this helps the Catholic case against gay marriage is a mystery, but they're welcome to make the argument — they're saying that contraception and divorce and artificial fertilization are all also crimes against nature. What a winning strategy!
3.

Lie about how awful homosexual parents are. Kids need both a mother and father, because mothers are nurturing and fathers are brave and disciplined. Yes, right, arguing from sexual stereotypes is OK if you're Catholic, and it also means you get to ignore the fact that a third of all households are headed by single mothers.
4.

Slippery slope! Some guy wanted to marry his horse, there are horrible awful polyamorous relationships, and even if you allow gays to marry, they don't all rush to the altar. This is a pointless argument: it's basically saying that we should only permit traditional 1 man:1 woman marriages because if we allow other possibilities, not all marriages will be between 1 man:1 woman. We also allow marriage between couples of different races, and a Catholic can even marry a Protestant — this has not led to a massive rush to marriages between a man, an oyster, a pelican, and a watermelon.
5.

Lie with statistics. This one is my favorite argument here. Gay marriage will hurt people! Did you know that 31% of lesbian report physical violence with their partner in the last year? (Don't mention the fact that 39% of women in a heterosexual relationship report domestic violence.) Gay men are more likely to be killed by a partner than a stranger! (Don't mention that heterosexual women are five times more likely to be killed by their partner than a stranger.)

Oh, and they do cite sources: most of them seem to be something called the Witherspoon Institute, which made a report…funded by the Templeton Foundation. Don't be surprised. Those rich jerks are pouring money into all kinds of dubious, religiously-motivated projects.

I'm beginning to wonder if Catholicism damages the brain: Ross Douthat also has a column on why gay marriage is wrong. It's not because gays are bad or unnatural, oh no — we must get away from the ghastly bigoted language and promote bigoted ideals more ambiguously. It's because relationships between men and women are specialer than those between men and men or women and women.

This ideal holds up the commitment to lifelong fidelity and support by two sexually different human beings — a commitment that involves the mutual surrender, arguably, of their reproductive self-interest — as a uniquely admirable kind of relationship. It holds up the domestic life that can be created only by such unions, in which children grow up in intimate contact with both of their biological parents, as a uniquely admirable approach to child-rearing. And recognizing the difficulty of achieving these goals, it surrounds wedlock with a distinctive set of rituals, sanctions and taboos.

The point of this ideal is not that other relationships have no value, or that only nuclear families can rear children successfully. Rather, it's that lifelong heterosexual monogamy at its best can offer something distinctive and remarkable — a microcosm of civilization, and an organic connection between human generations — that makes it worthy of distinctive recognition and support.

That's a non-argument. Of course opponents of gay marriage keep saying that heterosexual marriage is unique and special — but so what? They keep asserting that it's better and best and worthy of support, but no one is trying to say that men and women don't get to marry any more.

The whole problem is that we've got all the homophobes claiming that their favored kind of marriage is more admirable than any other kind of relationship, and so we must turn away from those other kinds of relationships. Hey, if you're looking for a "microcosm of civilization" of the kind I want to live in, it's not one where we quarantine and regulate love and tell people that they cannot love a rather large subset of the human race, even if it is reciprocated.

But then, that whole Catholic culture is one that I consider the antithesis of an enlightened and rational civilization, anyway.