"Nanny State" is a phrase used by a certain type of libertarian because they are mad that they can't smoke in Denny's anymore, and because Thomas Jefferson once said something about the tree of liberty being watered by super big-gulps. "Nanny State" is interesting because it is specifically describing the state as an authoritarian female. So lets look at two possibilities:

  1. Libertarians are dedicated to the idea that people are able to live best without interference, and that from both a philosophic and pragmatic point of view, trying to legislate morality will be counter-productive.
  2. They are ashamed that a woman will be in a position to find out what messy bad little boys they have been.

For me, Occam's Razor states that Libertarians are afraid that women will find out how much they like to poop themselves, and have invented an ideology to work around their psychosexual development, or lack thereof.