Reality-based conservatism

David Frum concludes that same sex marriage doesn't damage heterosexual marriage.

Is there anything else in American politics which is dependent on as weak an argument as opposition to same sex marriage? The war on drugs is based on a wild over-estimation of government power, but it doesn't quite have that weird "I'll make up a definition and insist that it's realer than what can be observed" quality.

Link thanks to nwhyte.