Personally I think Heinlein was too complicated to be a Libertarian and they are cherry picking his works. Heinlein was definitely into self reliant individualism but not as much into egotism as Libertarians seem to be. I would suggest Citizen of the Galaxy. I can't recall Libertarians mentioning that one.
psik
Heinlein had some libertarian tendencies, but you're right that he wasn't necessarily quite libertarian himself (some early stuff, like
Starship Troopers, is undoubtedly statist). But
Stranger in a Strange Land, for example, is claimed as libertarian SF by libertarians who read SF, in the sense that they see the book reflecting libertarian values and ideals.
Interestingly,
here's a list of libertarian SF compiled by io9, apparently with the input of actual libertarians. At least one of the choices is odd--LeGuin's
The Dispossessed, which is anarcho-syndicalist rather than libertarian. Anarcho-syndicalism is, in a sense, the "libertarianism of the left," in that it starts from a similar set of critiques of state power. But the solutions forwarded are as opposed to those forwarded by libertarianism as is possible from an anti-statist perspective.
I think you can also identify another strain of libertarian SF that is deliberately and ideologically libertarian. Authors like Larry Niven, Ben Bova, David Brin, etc. It's these authors who took the Heinleinian soup and crafted tropes out of it, e.g. "freedom-loving 'Belters vs. authoritarian Earthers." This is the kind of thing I noted that
LW reproduced (without necessarily sharing the political ideology of the forebears).
