The two issues are not the same: one is about who can get married, the other is about the nature of marriage.
The increasingly feeble efforts of opponents of equal marriage to find (apparently) non-homophobic grounds for their belief often seem to lead them to a slippery slope argument: if we allow gay people to marry then it logically follows that we have to allow polygamy too. No less a figure than John Roberts, the Chief Justice of the US Supreme Court, made this argument in no less a place than his dissent from his Court’s decision to legalise equal marriage.
More strangely, this argument has now been adopted by those of a more liberal disposition. Take, for example, this piece from the Economist arguing that:
Now that gay marriage is finally legal from sea to shining sea, it’s time for liberals to refine their arguments against polygamy. We need better, more rationally compelling arguments if we wish to be fair in shutting against would-be polygamists the libertarian door that we’ve just blasted open.
I confess I just don’t see the strong connection between the issues that proponents of polygamy and opponents of SSM do. In only the vaguest sense are the issues analogous.
For starters, the nature of those supposedly discriminated against is profoundly different. Being gay is an immutable and fundamental element of a person’s identity. Yes, most individuals probably have some fluidity as to their sexual identity but not enough to prevent a societal norm that one must be straight causing psychological damage to vast swathes of people. For this reason, virtually all legal systems treat sexuality as one of a number of characteristics (the others being race, sex etc.) that require special protection.
Desiring to marry more than one individual is not such a characteristic. It is an opinion or lifestyle choice that generally attracts no special protection from human rights law. It might be that those with religious motivations for their polygamy may be an exception because faith is generally a protected characteristic. However, if they could clear this hurdle they would face another.
Despite the frequent howls from its opponents that same sex marriage was a ‘redefinition’ of marriage, it actually leaves the institution itself almost wholly unchanged. What it does is allow access to the institution to those who were previously denied it. To give it legal effect all that is required is to replace gender specific pronouns in legislation.
In an article for the Atlantic, Conor Friedersorf explains why permitting polygamy would be a vastly more complicated matter:
….the legal institution [of marriage] is largely concerned with the “designation, without elaborate contracting, of a single other person third parties can look to in a variety of legal contexts.” Three-, four-, or five-person unions would require abandoning that aspect of marriage.
Americans can presently marry a foreign citizen and bring them here, after jumping through bureaucratic hoops, eventually sponsoring them for U.S. citizenship. Would the advent of plural marriage require that this practice be ended? Or would group marriages include the right to confer unlimited citizenships?
When I got married I was eligible to add my wife to my employer-sponsored health insurance. In a world of plural marriage, would this benefit of the institution end, or could I add as many people as I liked to my employer’s insurance plan?
If the parties to a plural marriage disagree about a medical decision that needs to be made on behalf of an unconscious spouse, who would get to decide the matter? Who would receive the Social Security survivor benefits if the patient died? These logistical matters add real costs to recognizing plural marriages––and they lessen the simplifying benefits that marriage confers on society. They also suggest that expanding the definition of civil marriage to encompass more than two parties is a far more radical, fundamental change than was recognizing unions of same-sex couples.
It thus follows that a prohibition on polygamy is not an arbitrary act of discrimination but a decision as to the nature of one of our most important legal institutions.
Which is not to say that polygamy is undesirable.* There is a big difference between saying something is not a human right and saying it is not right. However, that means it’s a subject for democratic debate. And as the ones advocating a change, the onus is on advocates of legal polygamy to provide positive reasons for allowing it. They cannot, as some hope and others fear, simply point to the advent of equal marriage and claim it necessitates their position.
*Though as it happens I would indeed make that argument.