I remember reading Citizen of the Galaxy at some point. It was very much an exploration of how spacer cultures could develop within the confines of their lifestyles (the Free Traders being insular and mostly closed off from the various planetside cultures, developing their own complex matriarchal society with limited social interaction to other people). Marrying cousins and altering definitions of family are common in books that do that. Like, in Citizen of the Galaxy they all call each other "cousin" or "uncle" or whatever, but they're not actually blood-related for the most part, if I remember correctly. C.J. Cherryh's Merchanter novels had similar themes going on where spacer crews are all big "families", at least those I read.
I wouldn't read too much into this sort of thing; especially not into the author's personal endorsement of such things, unless the personal life of the author suggests otherwise. When you write about small, tribal cultures mostly independent from others, in small confined spaces, the boundaries of incest will inevitably come up. Often it'll be described as weird to outsiders, because, well, it is. But it's also described as a necessity rather than just something they're into because they're weird, because they're insular communities.
Then again, with some other modern authors you get the feeling that they're really just trying to promote their own views and almost fetishes. Kim Stanley Robinson for example. Now I love the Mars Trilogy to death, I think they're fantastic books, but some of his later works tend to be, uh, not as good. The Mars Trilogy already had copious amounts of exploration of the extreme ends of free love mentality, especially from Green Mars onwards, but at least those books still tried to have a story. In 2312 Robinson just kinda forgets he has an actual plot and just goes on random tangents for hundreds of pages. Explorations of random types of interplanetary spaceships (massive hollowed out asteroids that are sent on orbits through the solar system, pretty cool concept) that all have completely random themes, like "Safari" or "massive fucking darkroom where travelling is a constant orgy". Not to mention that in space everyone is an artificial hermaphrodite and it is explicitly said that the best sex is between a dickgirl and a wombman because they get double the penetration each. Then there's a bit about saving Earth's ecology, and THEN he finally remembers that he actually had a plot about sentient robots going on. Still, Mars Trilogy ruled, despite also being very obviously influenced by his own political views.
"Pneumatic" was also used in Brave New World as a term for fit ladies, wasn't it? That term really needs to make a comeback.