As in the 2013 Hollingsworth v. Perry argument (here at 17: "What harm you see happening and when and how and--what--what harm to the institution of marriage or to opposite-sex couples, how does this cause and effect work?"), Justice Kagan asked yesterday (here at 44) why the expansion of the "marriage" label would undermine its effectiveness in its traditional applications:
It's the principal argument that you make in in your briefs, that same-sex marriage doesn't advance this State interest in regulating procreation. Let's just assume for the moment that that's so. Obviously, same-sex partners cannot procreate themselves. But is there in addition to that, are you saying that recognizing same-sex marriage will impinge upon that State interest, will harm that State interest in regulating procreation through marriage?
The idea was echoed by Justices Ginsburg (p. 44: "[Y]ou're not taking away anything from heterosexual couples."), Sotomayor (p. 46: "How does withholding marriage from one group, same--same-sex couples, increase the value to the other group?") and Kennedy (p. 49: "Same-sex couples say, of course, we understand the nobility and the sacredness of the marriage. We know we can't procreate, but we want the other attributes of it in order to show that we, too, have a dignity that can be fulfilled. ... [Y]ou're saying that this harms conventional marriage."). Kagan herself returned to the theme later, obviously dissatisfied with the response (p. 66: "[I]t's hard to see how permitting same-sex marriage discourages people from being bonded with their biological children."), as did Justice Breyer (p. 66-67: "What directly is your response to the fact that if we assume a basic purpose of marriage is to encourage an emotional and rearing bond between parents and children, that allowing gay people to marry will weaken it? ... [W]hat's the empirical connection?").
An analogy to trademark dilution, which I made in 2013 and David Crump made at much greater length in 2011, might, I think, explain the possible dynamics of "marriage" as a vehicle of social esteem a bit more crisply than did Michigan's lawyer, John Bursch. The Court explained in 1942's Mishawaka Rubber & Woolen Manufacturing:
The protection of trademarks is the law's recognition of the psychological function of symbols. If it is true that we live by symbols, it is no less true that we purchase goods by them. A trademark is a merchandising shortcut which induces a purchaser to select what he wants, or what he has been led to believe he wants. The owner of a mark exploits this human propensity by making every effort to impregnate the atmosphere of the market with the drawing power of a congenial symbol. Whatever the means employed, the aim is the same--to convey through the mark, in the minds of potential customers, the desirability of the commodity upon which it appears. Once this is attained, the trademark owner has something of value. If another poaches upon the commercial magnetism of the symbol he has created, the owner can obtain legal redress.
The suggestion here is not that the term "marriage" is not about social esteem at all--which Bursch at times seemed to say (e.g., pp. 71, 73)--but rather that the social esteem conveyed by a particular symbol can, at times, be a rivalrous good, subject to dilution when the symbol is more widely used. As Frank Schechter put it in 1926, trademark protects against the "gradual whittling away or dispersion of the identity and hold upon the public mind of the mark or name."
Dilution does not, of course, always take place. Brands may improve in value if new applications turn out to be better than old ones; if Pepsi is actually better than Coke, Coke won't be harmed, but benefitted, if Pepsi uses the "Coke" label. That benefit itself, however, depends on a link between the esteem conveyed by old and new applications of a symbol. If the Court regards the social science on the relative value of traditional and new applications of "marriage" as unsettled on Burkean millennia-versus-the-last-decade-Heller-v-Doe grounds--or at least as too unsettled and unclear for judicial review, see here and here--it should likewise be agnostic on the issue of harm to traditional applications.