Opponents of same-sex marriage reject it on religious and moral grounds but also on practical ones. If we let homosexuals marry, they believe, a parade of horribles will follow -- the weakening of marriage as an institution, children at increased risk of broken homes, the eventual legalization of polygamy and who knows what all.
Well, guess what? We're about to find out if they're right. Unlike most public policy debates, this one is the subject of a gigantic experiment, which should definitively answer whether same-sex marriage will have a broad, destructive social impact.
Massachusetts, Connecticut, Iowa, Vermont, Maine and New Hampshire have all decided to let gays wed. Most of the remaining 44 states, however, are not likely to follow suit anytime soon. So in the next few years, we will have a chance to compare social trends in the states permitting same-sex marriage against social trends in the others.
But with the experiment looming, some opponents seem to be doubting their own convictions. I contacted three serious conservative thinkers who have written extensively about the dangers of allowing gay marriage and asked them to make simple, concrete predictions about measurable social indicators -- marriage rates, divorce, out-of-wedlock births, child poverty, you name it.
You would think they would react like Albert Pujols when presented with a hanging curveball. Yet none was prepared to forecast what would happen in same-sex marriage states versus other states.
Maggie Gallagher, president of the Virginia-based Institute for Marriage and Public Policy, has declared that losing this battle "means losing American civilization." But she politely declined my invitation.
Stanley Kurtz, a senior fellow at the Ethics and Public Policy Center in Washington, has been equally dire. The change, he has warned, would weaken social taboos against adultery and incest and "set in motion a series of threats to the ethos of monogamy from which the institution of marriage may never recover."
When it came time to offer more specific predictions, Kurtz was missing in action. I e-mailed him twice and left a message on his office voicemail. After two weeks, I'm beginning to lose hope.