I’m listening to an episode of The Atheist Experience (#714, if you’re interested) wherein someone is tiresomely attempting to make the slippery-slope argument about gay marriage. First he tried to trap host Matt Dilahunty in hypocrisy by asking if he supported incest and/or polygamy, expecting the answer “no,” but Dilahunty gave the same answer I’ve given, which is that there’s no reason for the government to stand between consenting adults. He said he doesn’t see any reason to oppose incest between adults, provided they don’t conceive children, and he’s uncertain on polygamy (which, from a legal standpoint, I am too.)
The call then got really boneheaded as the caller alternately pretended Dilahunty hadn’t taken the wind out of his “hypocrisy” sails and accused him of supporting the slippery slope. Through the muddle one issue emerged: laws about marriage have changed in the past, and will probably continue to change in the future. The caller, and many people on the conservative side (using “conservative” here in the quite literal sense of “wanting to preserve current laws and customs”), use that fact as panic-fuel: if we change the laws about marriage in this way now, what’s to stop us from changing the laws about marriage in that way later?
What Dilahunty kept trying to communicate was that yes, laws have changed in the past, are changing in the present, and will probably change in the future, but in discussing and assessing each change, we are discussing that change only. Whether or not two women are allowed to marry is an entirely different question from whether or not two siblings should be allowed to marry, or whether or not one person should be able to marry three others, or whether or not a black person should be able to marry a white person. As society develops, ideas that were unthinkable become thinkable and then commonplace; ideas that were commonplace become suspect and then unthinkable. We change our laws to reflect our ideas. This happens all the time.
Now it’s true that most of us have a sense of morality that transcends the laws of our time. We’d better. Wherever your sense of morality comes from and however far it extends (personal, societal, humanistic, universal), the question whether to allow one form of marriage (or anything else) that we have previously disallowed still needs to be discussed on its own merits, without reference to any other form of marriage (or anything else) that is currently disallowed. The morality of allowing or not allowing same-sex couples to marry has nothing to do with the morality of allowing two siblings to marry. If, as a society, we ever being discussing the latter question, we will discuss it on its own merits.
The only thing incest, gay marriage, and polygamy have in common is that they’re all currently illegal in this country. Which makes me think that the slippery-slope argument comes from an ill-considered prejudice, an assumption that the laws and mores of one’s own time correspond to absolute morality. We’re accustomed to our society’s rules, they feel right and natural. But we are thinking beings with the ability to conceive of right and wrong apart from what feels natural to us; the ability to consider whether what “feels right” is, in fact, right by an external standard. This is an astonishing ability, one which few if any animals share to any degree. When faced with the question “Should same-sex couples be allowed to marry?” we can consider thoughtfully, weighing both the practical outcomes and the moral implications of the decision. Appealing to the slippery-slope argument is unworthy of us as a species.