Jeet Heer discusses Heinlein's political transformation in a 2014 essay on the New Republic. Heinlein was a socialist in the 1930s who flirted with the John Birch society in the 1950s, and became a Goldwater supporter in the 60s and a staunch libertarian thereafter.

As a young man, Heinlein supported himself through government assistance after being discharged from the Navy with a disability. In later life, he spoke out against "loafers" and the welfare state.

(What is it about prominent libertarians receiving government assistance? Heinlein, Ayn Rand, and I believe there were one or two others.)

The turning point came in 1957. After that year, Heinlein's books were no longer progressive explorations of the future but hectoring diatribes lamenting the decadence of modernity. A recurring character in these books—variously named Hugh Farnham, Jubal Harshaw or Lazarus Long—is a crusty older man who's a wellspring of wisdom. “Daddy, you have an annoying habit of being right,” runs an actual bit of dialogue from Farnham’s Freehold (1964). In the worst of Heinlein's later books, daddy not only knows best, he often knows everything….

Heinlein described some of his books as being “Swiftian” in intent. Regrettably, Heinlein lacked the rhetorical control of the Gulliver’s Travels author. Aside from a 1941 Yellow Peril novel, Heinlein had a strong record as a critic of racism. But in Farnham’s Freehold, Heinlein wanted to use inversion to show the evils of ethnic oppression: he took a middle-class white family and, via a nuclear explosion, threw them into a future where Africans rule the earth and enslave whites. So far, so good. Yet Heinlein’s Africans aren’t just a master race, they also castrate white men, make white women their concubines, and eat white children (white teenage girls being especially tasty). Preaching against racism, Heinlein resurrected some of the most horrific racial stereotypes imaginable. Farnham’s Freehold is an anti-racist novel only a Klansman could love.

Heer doesn't fully explore the weird sloppiness of "Farnham's Freehold." One of the characters in "Farnham's Freehold," which came out in the 1960s, is a young African-American working as a house-servant to the hero's family, the Farnham's. The young man is working his way through college and an accounting degree. Farnham lectures the young man on racism; the young man tells Farnham to STFU until Farnham has ridden a bus through the south as an African-American man.

And the African civilization of the future is a highly advanced, highly technological civilization. The Farnhams' master always speaks respectfully to the hero and treats Farnham kindly — by the standards of his day. Heinlein knew that some brutal civilizations were also highly advanced; the Romans and Spartans were certainly no pussycats.

But yeah cannibalism stealing white men's wives WTF?

There is a streak of American ethnocentrism, which is central to today's culture, that holds that all races and ethnicities are genetically equal but Anglo-American culture is the pinnacle of civilization. Asians, Africans, Jews and other non-Europeans can become good Americans if their cultural heritage is overwritten with the proper Anglo-European model. In its extreme form in the 19th Century you saw American Indian boys kidnapped from their parents and put in military schools designed to make them white; the motto was "Kill the Indian, save the man."

In its extreme form this is deplorable behavior — and yet it's isn't that the way the American melting pot works? I myself am a product of this process; my grandparents were Eastern European Jews who spoke Yiddish as their first language and heavily accented English. I'm an American who speaks only a few words of Yiddish, most of which I picked up from Neil Simon plays and such. And I am entirely pleased with that outcome.

Melting pot culture holds that everybody talks and acts the same, with a slight bit of variation for ethnic heritage. If you want a visual image, think of a Sikh man serving in the military: Turban, beard, and otherwise standard American uniform.

Heinlein and other science fiction of that period definitely corresponds to that school of ethnocentrism. In midcentury science fiction, Earth-people mapped to white Americans, and alien races were stand-ins for other races and nationalities of Earth. You see it in Star Trek too; the Federation and Starfleet are American-like institutions; other races, both human and alien, are free to participate so long as they act like white Americans. Even the aliens wear uniforms that look like human clothes.