In my last post on polygamy and same-sex marriage, I noted that Peter Ferguson and Colette Browne, in coming up with coherent arguments against polygamy, ended up acknowledging that marriage is to a certain extent about child welfare.

I wondered how a consent-based view of marriage could be reconciled with this, and I’m still not sure of the answer – but it was good to see that both Browne and Ferguson were OK with banning polygamous marriage because of the less-than-ideal circumstances for children of being raised by three or more parents.

But how are we to judge whether or not these detrimental consequences actually exist? Browne suggests, sensibly enough, consulting both history and scientific studies:

(Polygamy has)… implications for children too, with monogamous marriages being linked to lower rates of child neglect, abuse, accidental death and murder.

In short, there are many good reasons why most progressive, democratic, developed societies have outlawed polygamy but no similarly persuasive reasons why marriage remains illegal for gay couples.

Now, polygamy is an ancient practice (a salutary reminder to social conservatives that not everything that falls under the umbrella of ‘traditional’ marriage is worth defending). But let’s do a thought experiment and imagine that polygamy didn’t exist at all as a legal institution – but that multi-partner relationships with children did exist, but had only become reasonably commonplace relatively recently. 

Let’s further imagine that there was a movement among people in polygamous relationships pressing for the legal protection and recognition of marriage both for themselves and their children.

In such a scenario, would the burden of proof be on those supporting polygamy or those against it?  Obviously, in that scenario there wouldn’t be much available evidence to say whether polygamy was good, bad, or indifferent for children, but wouldn’t there be a pretty substantial burden to be overcome for those proposing to redefine marriage? Wouldn’t we laugh at anyone dismising objections to polygamous marriage as “polygamophobic?” I think we would.

Now, Browne and Ferguson argue that the burden of proof has been met in the case of same-sex parenting. Ferguson cites a considerable number of studies on his blog showing that same-sex parenting is more or less comparable to opposite-sex parenting, and both cite the variety of professional psychological bodies that have come out in support of same-sex marriage.

But in truth, reliable evidence regarding same-sex parenting is still very thin on the ground. The studies in this regard are almost always based on tiny or non-random samples or both. In the absence of much more compelling evidence (and in the presence of significant evidence showing that a marriage between one’s biological parents is certainly better for child welfare than a variety of other kinds of relationship), the burden of proof is on those who want to substantially change the institution of marriage. Mr Ferguson doesn’t think sample sizes matter all that much in psychological studies, and on this matter I just think he’s flatly mistaken.

And as for the psychological associations – need I remind Ferguson and Browne that the American Psychological Association regarded homosexuality as a mental illness until 1974? And if, as I hope most people would acknowledge, they were badly wrong then then, how are we so certain that they’re correct now? Scientific truth is not determined by committee.

To repeat, it is just too early to say what the effects on children of being raised by same-sex parents will be, and the burden of proof remains on those who support same-sex marriage. It’s worth noting that being raised by your married biological parents does seem to be better for child welfare than most other family forms, as Ferguson acknowledges (in the middle of another blog post criticising Iona, which are apparently his speciality):

The research shows that children fare best when raised by their own biological parents in a low-conflict marriage when compared to other family structures such as single parents, stepparents, and cohabitating parents.

Why would same-sex relationships be the exception to this general rule? Wouldn’t we have to have a pretty good reason for assuming that they are?

If legal polygamy didn’t exist, and a polygamous marriage movement demanded state recognition and insisted there would be no ill effects on children, we’d hardly just take them at their word, or be satisfied if they cited a few dozen small studies in order to justify such a major change to a very important social institution. We wouldn’t be particularly eager to knock down Chesterton’s Fence.

Why, then, are we doing precisely this with regard to same-sex marriage? I strongly suspect that it’s because the blogger Rod Dreher is right – that most of us have a priori beliefs about the nature of marriage, and that very few of us really make up our minds based on the evidence.