Libertarianism, at least big-L, doesn't quite fit Heinlein, I think. He isn't part of the deranged maximal-freedom thing that we now see in the libertarian movement and the ancaps that are running under that banner and he regularly espouses a socially aware, love-thy-neighbor attitude through his characters.

Heinlein always seems to have realized that, in a world with limited elbow room and the ability to fail very hard, government is both inescapable and actually valuable--and beyond the "blind arbiter of contracts" that you hear out of the libertarian bucket. I liked how Spider Robinson put it (although the article it comes from[1] is kind of fawning):

a man who bitterly opposes military conscription, supports consensual sexual freedom and women's ownership of their bellies, delights in unconventional marriage customs, champions massive expenditures for scientific research, suggests radical experiments in government; and; has written with apparent approval of anarchists, communists, socialists, technocrats, limited-franchise-republicans, emperors and empresses, capitalists, dictators, thieves, whores, charlatans and even career civil servants.

I'm not a libertarian (because I don't believe the strong should rule the weak, and I don't think Heinlein does either) and it's hard to find anything that in principle I can't be cool with.

[1] - http://www.heinleinsociety.org/rah/works/articles/rahrahrah....