I've just posted this article, which is forthcoming in the Hofstra Law Review. Here's the Introduction; for more details, and footnotes, see the article itself:

Recognizing same-sex marriage, some say, will make it more likely that the law will one day recognize polygamy. This is a classic slippery slope argument: Even if legal action A today (recognizing same-sex marriage) wouldn’t be that bad, or would even be moderately good, it should be opposed because it will increase the likelihood of a much worse legal action B in the future (recognizing polygamy). And the argument isn’t a logical one, but a psychological one: Though A and B are distinguishable, the argument goes, in practice it’s likely that various actors in our legal system — legislators, voters, judges — will eventually end up not distinguishing them.

Recognizing same-sex marriage, others say, will make it more likely that other “gay rights” laws will be passed and upheld, including laws that substantially burden religious objectors, institutions that are trying to further value systems that oppose homosexuality, or antigay speakers:

  • Employers (including churches, religious schools, and groups like the Boy Scouts) will have to hire homosexuals, even if they believe that the homosexuality is inconsistent with the employee’s position as a role model.

  • Private landlords will be required to rent to same-sex couples, even if the landlords have religious objections to providing space that would likely be used for sinful activity.

  • Roommates might be unable to advertise their preference for a same-sex heterosexual roommate.

  • Fear of “hostile work environment” liability under antidiscrimination law may pressure employers or educators into suppressing antigay views by employees or students.

  • Groups like the Boy Scouts may be required to have openly gay scoutmasters, or at least face exclusion from government benefits if they insist on limiting their leadership posts to heterosexuals.

This too is a slippery slope argument: Legal action A might not be that bad, for instance because giving same-sex couples marriage licenses doesn’t hurt anyone else. But taking action A will increase the chance of legal action B, which would be worse — from the perspective of some observers — because it would interfere with the free choice of people or groups who oppose homosexuality. (Naturally, some people might welcome the slippery slope, since they may favor B; but the argument’s target audience is those who oppose B.)

How can we evaluate the plausibility of these arguments? In this Essay, I’ll try to briefly discuss this question — and in the process, illustrate more broadly how slippery slope arguments can be made and analyzed.

Throughout, I’ll focus on examining the mechanisms behind the “slippery slope” metaphor. Metaphors are falsehoods. If they were literally true, they wouldn’t be metaphors.

Of course, metaphors are falsehoods that aim at exposing a deeper truth. They can be legitimate, and rhetorically powerful. Some of the most effective legal arguments use metaphor. Yet, as Justice Holmes cautions us, we must “think things not words” — “or at least we must constantly translate our words into the facts for which they stand, if we are to keep to the real and the true.” So what are the facts for which the metaphor “slippery slope” stands? To determine how likely it is that we will “slip” from one legal decision to another, we need to understand how the “slippery slope” operates, in fact and not just metaphorically.

What follows will not discuss (except briefly in the Conclusion) whether recognizing same-sex marriage is good or bad on its own terms; whether recognizing same-sex marriage is so morally or practically imperative that slippery slope arguments are irrelevant; or whether recognizing polygamous marriages or accepting broader antidiscrimination laws is itself good. These are all important parts of analyzing whether to support recognition of same-sex marriage, but I leave them to the many other commentators who are happy to deal with them.

Rather, I will focus solely on the empirical claims behind the slippery slope argument: that recognizing same-sex marriage will indeed help bring about those consequences. This is just a subset of the broader policy question, but I think an important subset, at least for those who like (or don’t deeply dislike) the first step A but oppose the possible future step B. And I think that exploring this subset can help illuminate slippery slope phenomena more broadly.