Jeff Jacoby

The federal court decision this month that struck down most of Utah's anti-polygamy law as unconstitutional is a fresh reminder that slippery-slope arguments, so frequently ridiculed, deserve more respect than they get.

"Conservatives foresaw polygamy ruling," a story in the Washington Times was headlined last week. It cited the "we-told-you-so" reactions of several longtime opponents of same-sex marriage, who have long argued that the radical transformation of marriage wouldn't end with gay wedlock.

"Sometimes I hate it when what I predict comes true," former Senator Rick Santorum tweeted after US District Judge Clark Waddoups held in favor of Kody Brown and his four wives, who had challenged Utah's ban on polygamy as a violation of their right to privacy. The judge's ruling still leaves plural marriage technically illegal in Utah, but only "in the literal sense" of having two or more marriage licenses. Otherwise, polygamy has now been effectively decriminalized in Utah — a state admitted to the union on the condition that it forever ban the practice of polygamy.

Not every change in law or policy is the first step down a slippery slope to a more drastic or unwelcome change. No one imagines that requiring a license for a pet dog today means you'll have to get a license for a pet fish tomorrow. But when a longstanding consensus on the meaning of a bedrock societal institution is altered — especially one as entwined with moral values and social attitudes as marriage — it is naïve or disingenuous to claim that even more extreme changes won't follow.

Yet time and again, advocates of same-sex marriage have pooh-poohed the warning that if marriage is redefined so that the sex of the spouses is irrelevant, it can be further redefined so that the number of spouses, or the family relationship of the spouses, is also irrelevant.

Jeff Jacoby

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