LGBT post, but there's a couple of things I wanted to add. I see this enormously bad argument made all the time: that opposing gay marriage is equivalent to opposing interracial marriage. And it bugs me. I plan on doing a post (or a series of posts) on gay marriage (and marriage in general---probably marriage in general first), but I just wanted to throw this out here while it's on my mind.
The power of this argument is obvious. Since there is absolutely nothing in the modern world worse than being a racist (which, regardless of what one thinks about race issues, is ridiculous in itself), equating opposition to homosexuality with racism puts the traditionalist on the defensive from the get-go. It's a fallacious claim, of course, but that's the power of these types of arguments: it diverts and trips up the opponent; it makes him prove it wrong because it's superficially plausible. So why is it fallacious? For many it should be obvious, but a short breakdown is probably necessary.
Natural law says that homosexual sex is immoral because it frustrates the natural end of human sexuality. Marriage is merely an extension of this principle. Natural law does not say that the purpose of sexuality is to just get semen into a vagina. That is just a basic minimum requirement. Instead, natural law argues that reproduction follows necessarily from this minimum requirement, and as such, marriage is a natural consequence of human sexuality. Or, that marriage and family are necessarily required for the flourishing of human beings. Or, that when a human being mates without another human being, he is good insofar as he protects and sustains that child, and he is defective or bad insofar as he doesn't. As homosexuality frustrates the natural end of sex itself, it has nothing metaphysically to do with the natural end of human sexuality: marriage. (This is just a quick overview; please hold back in-depth questions about marriage until a more comprehensive post.)
Now, interracial, heterosexual marriage would not frustrate the natural ends of sexuality and is perfectly in line with the end of human sexuality. Race is more akin to something like eye color. There is no defect in having a particular skin color or particular racial features, as they do not inhibit a human being's flourishing. There are certain disabilities that travel along with certain races (like sickle cell or something), but that's besides the point. Being white has nothing to do with human flourishing, and a white person is not better, in the metaphysical sense, than a non-white. Now, I think we ignore racial differences way too much or pretend that because we are metaphysically equal that we are necessarily physically equal (almost to the point of absurdity), but that's not really the point of this post. All I'm really trying to point out is that a black man having children with a white woman (or whatever), and their coming together to raise and protect the child, in no way violates natural law. Whether races should seek mixing, etc. etc. is a question completely outside the concerns of natural law.
As such, when a person opposes gay marriage, he is opposing something unnatural and immoral according to natural law, a metaphysical impossibility, a perversion of the basis of human flourishing. When he opposes interracial marriage, he is opposing something that has nothing to do with natural law. Whether or not he is opposing interracial marriage because of personal biases is not really what I want to go into. He may have legitimate cultural complaints. All I'm trying to point out is that his complaints have nothing, strictly speaking, to do with natural law morality. Even if he says, in both cases, that it's "unnatural," he is only right in the first case. Now, this isn't a gay marriage post necessarily; there is a lot that can be said about gay marriage. I'm just trying to point out where the comparison goes wrong. But it's important to point this out, for the reasons that follow.
This whole thing falls well within the LGBT v. The World narrative. As I noted in the LGBT post I think the purpose of this is to legitimize the conflict and take attention away from the actual underlying moral questions. People hate oppression (especially in the post-Christian West), and if you can equate LGBT with an oppressed group, then you're one step closer to convincing those same people that what LGBT people do is moral. As I noted, this is a complete sleight of hand.
What really bothers me about the whole thing is how much power is has as an argument. People are so terrified of looking like the oppressive group that they will backpedal as quickly as they can to avoid the controversy. And what's worse is that it's arguments like this that really get people going. It makes the whole thing political, completely separated from the underlying moral and cultural concerns. People will march in the streets over stuff like this, and how can anyone compete with that? When we're at the "civil rights" movement stage, discussion is over. And as everyone knows (because their Kindergarten teacher told them so), anyone who pushes for civil rights is ultimately correct. The whole thing turns a legitimate moral position into "hate." It's a pretty impressive thing really.
In many ways I can't tell how convincing this argument is outside the mobs of protesters. I mean, decent philosophers who support gay marriage have to realize that this comparison is faulty. But at the same time, I don't know. I come across it all the time. And I only rarely hear people say "well, no, one is immoral and the other one wasn't." If they do, the usual retort is, "well, they thought interracial marriage was immoral too!" Then it devolves into a sort of emotivism back and forth until everyone is throwing food.
Now, there is one thing about the argument I can agree with: part two, which I said is "that it's inevitable that change will happen and people today will be the bigots of yesterday." This will happen. People will say this. I don't really have any doubt about it. Now, this will of course be a completely unjustified slander, but that's the way it's going to be.