When I read this book by Robert Heinlein, over 40 years ago, I thought what a shame that there wasn't some like Valentine Micheal Smith to show people a better way of living with each other by teaching them the Martian language.
Some of the ideas from that book were transforming to society like the invention of the term Grok meaning to understand so thoroughly that the observer becomes a part of the observedâ€”to merge, blend, intermarry, lose identity in group experience.
But since then I have found some ways those ideas could be implemented without some of the drawbacks like having to find advanced ETI cultures or Smith getting martyred for his cause.
Instead of the fictional Martian language, it could be replaced by the more practical map described as The Integral Operating System that would serve a lot of the same purpose but more easily grasped and with more flexibility in it's use.
Instead of unwieldy use of religion in the "Church of All Worlds" it could be replaced by the more straight forward Integral Life Practice that has much less dogma and can be shown to work by experience
Much of the essence of the rituals like the "Sharing Water Ceremony" are still contained in the practices of Tantra Yoga which is what Heinlein used as a foundation for that book so that wouldn't alter it significantly from the book
I went to hs with a close relative of his She told me things I did not want to nor enjoy hearing about one of my favorite authors. He was a literary genius. I'd prefer to not know about his obsession that expressed in his later novels.
The point Heinlein was trying to make about what you termed his "obsession" was the origin and biological reasons for some cultural taboos would become outdated with medical advances in genetics.
Once the basis for those taboos were eliminated even those that had lived for thousands of years would have to adjust to the effects those advances had to give up the conditioning of the society that they were raised in because they no longer applied to the current culture.
The IOS goes into this by proposing a Basic Moral Intuition which is to protect and promote the greatest depth for the greatest span