To be honest, I'm not really sure what "social conservative" means. If it's just a synonym for impulse control, then you'll find that libertarians tend to be socially conservative in their personal lives. The idea that an absence of government mandates necessitates a culture of individual responsibility is well understood and appreciated in libertarian philosophy. On the other hand, it's unclear if Paul Rahe is using the term "social conservative" to mean advocacy for government prohibitions on individual behavior, such as drug use or homosexual relationships. This would lead to a fundamental contradiction for libertarians, like the "freedom is slavery" newspeak of the 1984-world: give government more control so that government isn't as necessary. The appropriate means of encouraging societal impulse control, to me, are establishing a strong moral culture that rejects ends-justifying-the-means progressive utilitarianism, and setting up civic institutions so that individuals bear the consequences of their own destructive behaviors rather than being automatically bailed out by a faceless and shameless administrative bureaucracy. An individual-responsibility culture has always been the alternative to the state suggested by libertarians, but to use the force of the state to prohibit individuals from self-destruction would be to violate the non-aggression principle at the heart of the philosophy itself.