Please note: Title intentionally inflammatory to increase readership. In fact, the point of this is to try to provide a more well-reasoned attack on Proposition 8 than we usually see. Liberals, myself included, have expressed a generally unintelligible ire over Prop 8 while conservatives generally sound reasoned and principled on the subject. I think a proper analogy is asking the man who's just been stabbed in the gut to perform an oratory on the evils of assault. We're just too angry and wounded to do it, and it looks like the rationale should be obvious. Let me try to parse it out in a bit more methodical way than just "YOU CAN'T DO THAT!".
The right for the government to curtail people's sexual choices in their private lives is self-evident. You can't have sex with children, you can't have sex with someone who doesn't consent, you can't sell your own body for sex, etc. There's no fundamental philosophical rule behind any of these rules. Kant doesn't say kids aren't okay but people of your gender are, and Locke doesn't contend that there's some fundamental rule that says same-sex marriage is wrong, but heterosexual marriage is right. It's indefensible to claim that the government can't restrict a person's private sexual choices, and that's true for both sides of the aisle.
An applicable analogy: strong defenders of the second Amendment often decry assault weapons bans because the government shouldn't abridge anyone's right to bear arms. It stands to reason that they should also allow a private actor to build his own nuclear weapon, as barring that would violate the sacrosanct second amendment. No one in their right mind would defend that, but it sort of disproves the notion that people really believe in a fundamental right for private entities to break the state's monopoly on violence. They support the principle, but not its full enactment, because that would lead to total chaos. It's about where you draw the line.
The same is true for private sexual choice, but it becomes a question of where we draw the line. Until 1967, it was drawn here: in 16 states, you could only marry someone of a different gender, but the same race. These states had centuries-old anti-miscegenation laws, backed by popular majorities, on the books. All 16 of these states' laws fell when the Supreme Court ruled unanimously in Loving v. Virginia that anti-miscegenation violated the equal protection clause of the 14th amendment. Today, we all generally recognize that putting the line there was both arbitrary and wrong.
Whether it is wrong to restrict same-sex couples is apparently open for debate, but it is an untenable position to claim that it is not arbitrary. Some say it follows their religious convictions, and while the Bible does take a strong stance against homosexuality, here are a handful of Biblical passages that a philosophically sound Christian would also want to translate into law:
Malachi 2:16: “I hate divorce, says the Lord God of Israel.”
Exodus 22:16-17: "If a man seduces a virgin who is not pledged to be married and sleeps with her, he must pay the bride-price, and she shall be his wife. If her father absolutely refuses to give her to him, he must still pay the bride-price for virgins."
Deuteronomy 7:3-4: "Do not intermarry with them. Do not give your daughters to their sons or take their daughters for your sons, for they will turn your sons away from following me to serve other gods, and the Lord’s anger will burn against you and will quickly destroy you."
Anything short of banning divorce, premarital sex without immediate marriage afterwards and interfaith (arguably interracial) marriage is the philosophical equivalent of cherry-picking the Bible. As someone who is admittedly not a firm believer in the Bible, I'm okay with this. Again, it's a question of where you draw the line. To generalize a majority of religiously-motivated people, here's the line: premarital sex—not good, but not illegal; divorce—not good, but not illegal; interfaith marriage—not ideal, but not illegal; gay marriage— illegal.
In terms of the religious argument, my default is to return to the word "bigot." Biblically proscribed heterosexual practices are okay, but those involving homosexuals are not. The religiously-backed line is and must be arbitrary, but must it preclude gay marriage?
Let's look at another common argument: the slippery slope. Among the more amusing lines of argumentation to hear, this analysis contends that redefining the meaning of marriage to include homosexual couples opens the floodgates to legalizing pedophilia and bestiality. Although I disagree, I see the logic. But it bears asking, where is the original definition of marriage, and is there anything else we allow that might have already triggered that slippery slope? At our nation's inception, marriage was a union between a white man and a white woman. It was not until Reconstruction (briefly), and then the aforementioned court case forty years ago (permanently), that we "opened the floodgates" by allowing interracial marriage. There, the line of acceptable practice moved, and we have not noticed a major shift since. Again, this was an arbitrary judgment based on valuing the social importance of civil liberties over the philosophical tenet that we should not alter the meaning of marriage. We redrew the line to include interracial marriage without allowing gay marriage, underage marriage or bestiality. We could have, but none of those positions seemed socially tenable. Recap: interracial marriage—fine, gay marriage—illegal.
This brings us to the ultimate, most important question. If it's a logical truism that our restrictions on private sexuality are arbitrary, should this arbitrary line preclude gay marriage because it is socially harmful? I think this is where most of the debate ought to lie. I'm personally of the opinion that homosexual couples are doing no harm to society. Here are some points upon which I base this judgment.
1. Children of homosexual couples turn out almost exactly the same as those of heterosexual couples.
2. A broad consensus of major children's health and welfare organizations oppose restrictions on gay marriage.
These are just two of many points that represent a pretty solid consensus that a consenting adult marrying another consenting adult of the same gender doesn't hurt anyone. I personally believe that this wealth of evidence is convincing and perhaps even overwhelming. And that's why my default response to opponents of gay marriage is to call them "bigots." As established, the line is arbitrary. So if someone draws that line, in the face of strong evidence that it's not a good idea, to preclude gays from marrying, I have to assume it's based on raw prejudice. I see the counter-arguments, but I don't find them compelling. If you can present me with some good ones beyond those which I've already outlined here, feel free to drop a comment. Until then, I'll hop on my pinko commie high horse assume you're an ass-backwards, narrow-minded backwoods bigot.