I was recently struck by how a similar line of argument arose in two places: the British Museum’s position on the Elgin Marbles, and Chief Justice Roberts’s opinion on Obergefell v. Hodges.
Part I: The Marbles
The Elgin Marbles (or “Parthenon Sculptures”) are a some pieces of the Parthenon in Athens that were removed by the Earl of Elgin in 1801. Lord Elgin was the British ambassador to Turkey (a.k.a., the Ottoman Empire), which controlled Greece. (Greece had been under Ottoman control for hundreds of years, but it would soon break way in the Greek War of Independence, which started in 1821.) There’s a lot of controversial history here, but it seems like Elgin got the approval from the Ottomans to remove the sculptures. He shipped them back to Britain, and they ended up in the British Museum, where they now remain.
The Greeks have asked the Museum to return the sculptures to Greece. The Museum’s official position is fairly simple: “The Parthenon Sculptures are a vital element in [the Museum’s] interconnected world collection. They are a part of the world’s shared heritage and transcend political boundaries.” Very roughly rendered: if we gave them back, it would ruin the Museum, and anyway you don’t have any greater claim to them than we do.
I think a fear behind the Museum’s position and behind the position of other anti-restitution/pro-keep-it-where-it-is advocates (e.g., Dorothy King) is that if the museum gave the Elgin Marbles back, they might have to give lots of other stuff back.
Part II: Gay marriage
One part of Chief Justice Roberts’s dissenting opinion is about polygamy.
It is striking how much of the majority’s reasoning would apply with equal force to the claim of a fundamental right to plural marriage. If “[t]here is dignity in the bond between two men or two women who seek to marry and in their autonomy to make such profound choices,” ante, at 13, why would there be any less dignity in the bond between three people who, in exercising their autonomy, seek to make the profound choice to marry?
After some more discussion, he concludes:
I do not mean to equate marriage between same-sex couples with plural marriages in all respects. There may well be relevant differences that compel different legal analysis. But if there are, petitioners have not pointed to any. When asked about a plural marital union at oral argument, petitioners asserted that a State “doesn’t have such an institution.” Tr. of Oral Arg. on Question 2, p. 6. But that is exactly the point: the States at issue here do not have an institution of same-sex marriage, either.
Justice Roberts says that his point is that the States don’t have institutions of gay marriage or plural marriage, so doesn’t make sense to allow one without the other. I think, though, that a more important motivation for Justice Roberts is something more visceral: if we legalize gay marriage, then we might as well legalize polygamy.
Part III: Not quite a slippery slope
Both of these arguments sound, on the surface, like slippery-slope arguments: if we do (or allow) X, then eventually Y will happen. I think it’s more accurate though, to see these as “arguments of equivalent repugnance”. (I made up this term. It’s not reductio ad absurdum, but it has a similar flavor.)
In a slippery-slope argument, a little action X leads to a result that leads to a slightly larger action that causes a terrible result Y. In the Elgin Marble case, this argument sounds like: if we give back the Parthenon sculptures, we set a precedent, then other people will ask for everything back, this re-enforces the precedent, and eventually we have no Museum, which is bad. In the gay marriage case, this argument sounds like: if we legalize gay marriage, that will break the old definition of marriage, and then people will want to get married in all sorts of configurations, and we’ll have to legalize all of those, which is bad.
These (straw man) arguments imply that the watchdog will enter an eternal slumber after this one judgement. If the Museum gives back the Marbles, those same people in the Museum would suddenly turn into pro-restitution advocates; if the Supreme Court legalizes gay marriage, then society as a whole, including the Court, will turn into people who think plural marriage is OK.
I think the emotional content of the objections in Parts I and II can’t be anything as processual and incremental as these slippery-slope arguments. I think it’s mostly about a sense of equivalent repugnance. Because giving back the Marbles could be related to the dissolution of the Museum, and the dissolution is repugnant, we should view the return of the Marbles with equivalent repugnance. Because same-sex marriage and plural marriage share some legal properties, and plural marriage is repugnant, then same-sex marriage should feel equivalently repugnant.
Slippery-slope arguments are about the final outcome. Arguments of equivalent repugnance are about the first thing in the chain. The same logic that could lead us to return the Marbles could lead us to empty the Museum, so we should do neither. The same arguments that apply to same-sex marriage could apply to plural marriage, so we should reject them.