The Supreme Court ruling in Obergefell vs. Hodges dictates that states cannot prevent same-sex couples from marrying and requires them to recognize such unions, but it’s been met with some expected criticism. The argument can be simply summarized by Justice Alito’s comment, “well then why not marry four gay men together? Why just two?” In effect he’s saying, “well, if gay marriage is legal, why not polygamous marriage? Why place any limitations on who can get married at all?”

The core reason this isn’t a valid argument against gay marriage is pretty easy to spot—the decision is about gay marriage, so it makes no sense to oppose it on the basis of a completely different issue—but, there is a more valid moral point that requires some deeper consideration.

It’s a fantastic step for the rights of Americans in same-sex relationships, and one that should rightly be applauded, but is there really a moral justification for preventing other people in “non-traditional” relationships from getting married? Contrary to how compelling such arguments may seem, the basic fact is: the Supreme Court ruling does not open the door to polygamy any more than “traditional marriage” does. The problem really comes from a definition of marriage that doesn’t stand up well to scrutiny.

The Slippery Slope

First off, the core reason this is not a valid argument should be emphasized. It’s an example of a slippery slope: an argument that runs “if A happens, the next thing you know, Z will have happened,” working entirely from a complete refusal to acknowledge that there are 24 intermediate steps between those two end-points and that each one represents a separate decision.

The anti-gay marriage slippery slope argument is such a common and characteristic one, it’s even used as an example on sites teaching the fallacy. In short, allowing gay marriage doesn’t logically necessitate anything happening other than allowing gay marriage, because decisions need to be made every step of the way.

The Differences Between Gay Marriage and Polygamy

Of course, the arguments put forward by opponents of gay marriage are more nuanced than this. In the wake of the decision, critics pointed out how the arguments of the proponents of gay marriage could often be applied to polygamous marriage, and the decision to change the “man-woman” element of the definition of marriage is really no different to changing the “two people” element.

One of the key points raised in support of gay marriage is written by Justice Anthony Kennedy as “the right to personal choice regarding marriage is inherent in the concept of individual autonomy.” This does clearly apply to polygamists too, as do arguments centering on how anti-gay marriage laws demean gay and lesbian people and “humiliate the children of same-sex couples.” There is a genuinely strong moral argument that suggests that we should consider treating those in polygamous relationships with the same respect.

There are many crucial differences between homosexuality and polygamy in the context of marriage, though, which show precisely why the “slippery slope” argument is invalid. The first is that otherwise, homosexuals couldn’t get married to their partners at all. Polygamists are perfectly free to enjoy the protections and benefits of marriage by marrying one partner and merely living with the other, and larger groups could arrange things so—at most—one individual is left unmarried. Homosexuals, on the other hand, would not get to enjoy the benefits of marriage—including tax breaks, property rights, adoption rights and much more—at all without a change being made to the definition of marriage.

Similarly, as Justice Kennedy writes, “Marriage responds to the universal fear that a lonely person might call out only to find no one there.” Gays, lesbians and bisexuals were previously condemned to loneliness (from a purely legal perspective), but polygamists—for the reasons outlined above—aren’t being legislated into solitude in this way.

In fact, allowing polygamous marriage could result in more people living in solitude. Polygamous marriage allows high status men or women to take multiple partners, and this invariably leaves those of lower status without anybody. This is the stated explanation for the higher levels of rape, kidnapping, assault, murder and robbery in polygamous cultures. In short, polygamy increases competition and social problems by reducing the number of mates there are to go around.

There are many other similar arguments. For example, it’s widely accepted now that homosexuality is an “immutable” (unchangeable, innate) characteristic—i.e., gays, lesbians and bisexuals are “born that way”—but this is not accepted of polyamory. Whether it’s true is another matter, but it’s not accepted as such in wider society. In fact, it can be argued that one of polyamory’s greatest issues is acceptance—while gays, lesbians and bisexuals have been gaining acceptance and understanding for decades, the same can’t be said of those taking multiple partners.

Finally, the logistical differences between allowing gay marriage in legislation and allowing polygamous marriage are also notable. Gay marriage, gender aside, is identical to straight marriage—the only change required is for gender-neutral language to be used—whereas polygamy is fundamentally different. For some simple examples: who is married to whom? Is each member married to every other member? Is one member married to all other members? Who do you turn to for medical decisions? Who gets custody of the children in the event of a divorce? Clearly, allowing polygamous marriage is a huge step; allowing gay marriage is comparatively easy.

Conclusion—Polygamy Isn’t Wrong, But it Has Nothing to Do With Gay Marriage

None of this goes to say that polygamy is wrong. What happens between consenting adults is nobody’s business but theirs, and nobody should dictate which relationships are “acceptable.” However, enshrining this in law is a different matter entirely and one that is notably distinct from gay marriage in many ways. Your moral support of (or opposition to) polygamy is not defined by your position on gay marriage, even though the broader (and compelling) arguments for equality for people regardless of the type of relationship they prefer do still apply.

The real reason the gay marriage issue brings up polygamy is a simple one: it requires us to look at and think about what we mean by marriage, and the decisions we’ve made about who should be allowed to get married. The thing that could really “open the door” to polygamy is that process of looking at the assumptions underlying marriage law. If we’d chosen to do that prior to the acceptance of gay marriage, paying no consideration to gender, would it really have been such an unimaginable suggestion? Not at all. It’s a question you could envision a child asking: “Daddy, why can people only get married in twos?”

Gay marriage gets the blame for the widespread asking of this question only because it requires us to do the same thing: take a look at the morality of current marriage law and consider whether it could be changed. If that opens up some valid questions about whether we should be discriminating against polygamous relationships, then it’s hardly the fault of a completely separate issue just because it prompted us to critically examine our laws.

The reasons gay marriage has gained traction but polygamous marriage hasn’t are: 1) gay marriage is simpler 2) homosexuals couldn’t get married at all otherwise and 3) homosexuality is more widely accepted. There are fundamental differences—and several issues—that may prevent polygamy from being similarly accepted for a long time, and allowing gay marriage doesn’t necessarily mean anything for polygamy.

However, even if polygamous marriage was accepted immediately afterwards, the decision wouldn’t have anything to do with allowing gay marriage, it would be about the more important, underlying issue of trying to build a more inclusive and less discriminatory society. If that means dispensing with tradition, then so be it.