We must consider what single-sex marriage commits us to

Every week I seem to say something on Twitter that is almost universally misunderstood. Last week I said that there was nothing of value in equality per se, which many took to mean I was a right-wing lunatic.

This week I said that if we commit ourselves to allowing single-sex marriage, consistency demands that we also commit ourselves to a wider range of other sorts of marriage, sorts that we have hitherto disallowed. For example, we might allow some incestuous marriages.

Cue moralistic outrage. “You’re equating homosexuality and incest!” — “Slippery slope arguments are fallacious!” — “You’re a dirty homophobe for opposing single-sex marriage!” And so on.

First, I’m not “equating” homosexuality and incest at all. They’re obviously completely different. Most homosexual acts are morally neutral, whereas most incestuous acts are morally wrong. But both are routinely observed in the sexual behaviour of many species. Although they are “minority” activities, they are recognisably common — enough to be described as biologically “normal”.

Second, many slippery slope “arguments” (if they count as arguments at all) are not “fallacious” (if that’s the appropriate word). We often do have reason to believe that small initial changes portend much larger changes to come. A hundred years ago, opponents of universal suffrage argued that women should not be allowed to vote, because that would open the floodgates to all sorts of social changes. And they were right. It did lead to all sorts of social changes, most of which most of us warmly welcome.

But in any case I’m not worried at all about any slippery slope, nor am I warning of any such thing. Incestuous sex will always be a minority activity, and genuine, consensual incestuous love so uncommon that very few will ever want to seal their relationship by marrying each other. There are no “floodgates” about to open here.

Third, I am not opposed to single-sex marriage. (Nor would I be a “homophobe” if I were.) Rather, I’m trying to draw attention to some other commitments we inevitably take on if we are consistently committed to single-sex marriage.

Single-sex marriage is justified by a principle. That principle goes something like this: “if two consenting adults want their relationship to be recognised and sealed by law as marriage, the rest of society should not prevent them doing so”. If we deny consenting adults the legal right to marry, we are guilty of discrimination of a morally wrong sort. And it’s quite seriously wrong, I would argue, because the desire to marry — to marry the person one considers the love of one’s life — is a central part of human life and human flourishing.

Avoiding discrimination means “turning a blind eye” to differences, at least in law. We deliberately allow our commitment to a moral principle to override any personal distaste we may feel for people who are different in the way we are now deciding to treat as irrelevant.

By allowing people of the same sex to marry, we choose to override any distaste we may feel for homosexuality. (There must be some who feel such distaste, as we are told homophobia is so common.) We choose to treat their incapacity to procreate as irrelevant. We do the same for older people, or people who are barren for other reasons. We allow people who carry genetic diseases to marry, even though we know that if they were to procreate, their children may suffer serious disability. Our commitment to the above principle — a humane and decent principle guided by respect for erotic love — leads us to treat biologically ill-starred conditions as legally irrelevant. And a good thing too.

One such “ill-starred” condition is exemplified by Siegmund and Sieglinde in Wagner’s opera Die Walküre. As brother and sister who were separated when very young, they don’t recognise each other when they meet again as adults. But their instant affinity quickly grows into full human love. This love is not diminished by the discovery that they are siblings.

That sort of situation in common in mythology, scripture, and art. Incest is probably more common in such stories than homosexuality. However much we may disapprove of it, incestuous love must surely occur in real life, especially with recently increased fluidity of families, greater frequency of separations in childhood, larger numbers of step-parents and half-siblings, and so on.

It seems to me that denying siblings the right to marry is an anachronism, or at least it will become an anachronism as soon as we allow homosexuals to marry, as I think we should. It conflicts with the basic principle that we commit ourselves to by allowing single-sex marriage.

Of course it is appalling that some parents rape their children. Of course the legal right to marry should be strictly limited to consenting adults. Of course consent cannot be given by an adult who is mentally ill or the traumatised victim of abuse. These things go without saying.

But as we consider the question of single-sex marriage, we should consider the broader possibilities that our guiding principle opens, and the wider commitments we are obliged to take on. It doesn’t matter that very few siblings or half-siblings will ever want to marry. That fact that some of them will is enough. We are obliged to consider the possibility, and what our response should be.

What I have learned in the past week is that the quality of debate over single-sex marriage is wretched. Well-meaning but unintelligent journalists pour politically correct syrup over real issues, and chicken out of robust debate with anyone who doesn’t accept their relentlessly and predictably orthodox views. I have no distaste for homosexuality myself, but I’m growing increasingly impatient with a “gay lobby” whose idea of debate is cheap victim-stancing or aggressive accusations of homophobia.