Measuring the Impact of Gay Marriage

This is a great point (via Conor Clarke):

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.

I'm in favor of gay marriage, but I don't think we should simply dismiss those who oppose it on practical grounds. Perhaps gay marriage will adversely impact the rate of heterosexual marriages or subtly encourage other social problems. Those of us who support gay marriage may be confident that homosexual unions won't generate any serious social side-effects, but this is really an empirical question, isn't it?

And that's the beauty of federalism. We now have social experiments in progress.

So, instead of fear-mongering, why don't opponents of gay marriage simply make their predictions known? Will gay marriage have a "destructive social impact" or not?

If you think it will, what should we expect . . .?