Jeff Jacoby

It was during oral arguments in Hollingsworth v. Perry, one of two same-sex marriage cases the Supreme Court took up in March, that Justice Sonia Sotomayor raised the inescapable question, the one that has always loomed over the campaign to radically redefine marriage: Where would the changes end?

"If you say that marriage is a fundamental right," Sotomayor challenged Ted Olson, the lawyer urging the court to invalidate California's Proposition 8 defining marriage as the union of a man and a woman, "what state restrictions could ever exist?" If the Constitution won't permit marriage to be limited to spouses of the opposite sex, then how can it allow "state restrictions with respect to the number of people … that could get married" or "the incest laws?" Presumably states would still be free to ban child marriages, she said, but other than that, "what's left?"

In other words, if it's arbitrary and unjust to forbid same-sex marriage, isn't it just as arbitrary and unjust to forbid plural marriage? Or sibling marriage? Once the right to "marriage equality" is enshrined in law, how could any union of consenting adults be denied a marriage license, regardless of traditional norms or definitions?

There is nothing new about this concern, of course. Opponents of same-sex marriage have sounded it for years. Frequently they were accused of pandering to bigotry, or engaging in slippery-slope hysteria. "This is not an argument, it's a panic," wrote Andrew Sullivan, one of the earliest champions of same-sex marriage, in 1996. "To the best of my knowledge, there is no polygamists' rights organization poised to exploit same-sex marriage to return the republic to polygamous abandon. Indeed, few in the same-sex marriage camp have anything but disdain for such an idea."

Sullivan's mocking putdown may have been effective a decade and a half ago. Even now many gay-marriage advocates are inclined to smear as "haters" and "homophobes" those who warn that the drastic revision of marriage won't end with same-sex weddings.

Yet today the avant-garde of "marriage equality" has moved far beyond merely demanding that two men be allowed to marry, or two women.

Jeff Jacoby

Jeff Jacoby is an Op-Ed writer for the Boston Globe, a radio political commentator, and a contributing columnist for