One of the claimed benefits for federalism in the U.S. is that differences in state public policy provides natural experiments by which to empirically assess the cost and benefits of alternative policies. Writing at Reason, Steve Chapman points out that differences in state policies towards gay marriage is about to provide just such an experiment:
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.Read it all.
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 have a strong suspicion that both sides of the debate are right. The supporters of same-sex marriage are right in predicting that it will have no bad side effects. And the opponents are right not to make predictions.