Heinlein

A couple points:

There is a great degree of variation among libertarian beliefs, even "pure" libertarian beliefs. They may all stem from the same basic core idea of never initiating force, but they can quickly branch out from there to support opposing views: e.g., in the abortion debate, does one support the right of the mother to make her own decisions about her body, or does one support the right of a fetus to not be killed? (The latter surely being an initiation of force.) In this, and other cases, the principle of non-initiation of force must be informed by other factors, such as whether a fetus has standing as a human being or not - and on such points, libertarians often disagree.

It should also be noted that at the time that Heinlein was flirting with socialist ideas, virtually every young intellectual in America was doing likewise. Most of them - including Heinlein - abandoned socialist ideas after a few years - in part or in whole - after seeing problems with them. Many people espouse ideas in their twenties that they strongly disagree with later in life, so it would be unreasonable to attach too much weight to Heinlein's early beliefs.

The author does have a point that Heinlein might have adapted to the political views of his wife-of-the-moment, as Heinlein himself sort of suggested such a view in several of his books. Of course, his own views doubtless affected to some degree his choice of wife at different points in his life.

All that said, Heinlein himself resisted being pigeonholed as a libertarian or anything else. Mostly he reflected the cultural values of his place and time, modified and expanded by his own experiences and prodigious intelligence. As American values of that time had a strong libertarian component, it should come as no surprise that his writings reflect that.