Just when you thought the marriage debate had been settled – in favour of same-sex marriage (SSM) – along comes an even more contentious issue. Not so long ago the idea that SSM could or should pave the way for polygamous marriage was a fringe concern. However, the debate is now moving into the mainstream.

For instance, the Economist – a longstanding supporter of SSM – recently invited Professor Stephen Macedo of Princeton University to make the case against the legal recognition of polygamous marriage.

Far from advancing the cause of equality, Macedo argues that polygamy is traditionally associated with inequality:

“The vast majority (85%) of the polygamous societies studied by anthropologists reveal the arrangement to be a marker of privilege and high status…

Also, won’t anyone think of the children?

“Complex plural families—composed of multiple wives and children related as half-siblings—are prone to jealousy and conflict. Even accounts sympathetic to polygamy identify jealousy as a big problem, and diminished genetic relatedness is a risk for sexual abuse. Polygamous families are characterised by much higher levels of violence and stress in the home, as well as worse health outcomes for women and children.”

This overlooks the fact that western societies already practice – and to some extent officially sanction – polygamy. Our liberal divorce laws not only enable one person to marry a succession of partners, but also ensure that legally enforceable obligations to each ex-spouse continue after the marriage itself is dissolved. In this and other regards, the state does recognise, and intervenes to support, “complex plural families”, especially when children are involved.

However, if the adults in such families wish to be married to one another concurrently, then the law obstructs instead of enables. There is a difficulty here for liberals who hold to the principle of parity of esteem for different kinds of families, because turning round to one kind of family and telling them that they are unworthy of marriage is surely a moral judgment.

It should also be said that not all polygamy is rooted in traditional cultures. There is, for instance, the practice of polyamory – “the name given to egalitarian adult romantic networks.” Given that we recognise same-sex marriage for couples who want it, why shouldn’t we extend the same right to polyamorous threesomes, foursomes and moresomes?

Macedo’s debatable answer is that there’s no call for it:

“The evidence of polyamory is entirely a matter of anecdote, speculation and free-love advocacy. In no Western society is there any broad social movement for polygamous or ‘polyamorous rights’ equivalent to the decades-long struggle for the rights of gay, lesbian and transgendered citizens.”

Writing in the New York Times, William Baude makes an interesting counter-argument:

“…the lesson of the same-sex marriage case is that we should not be too wedded to historical assumptions. It was not that long ago that many people held vicious stereotypes about same-sex relationships that led them to wrongly assume that gay people were unfit for marriage. We should not make the same mistake in assuming we know what plural marriages in the future would be like.”

Personally, I don’t like the idea of polygamous marriage, but within a secular and liberal frame of reference, I couldn’t tell you why people who do shouldn’t get their wish.