"My dear, there are aspects of sex of which it is impossible to communicate between the two sexes of our race. They are sometimes grokked by intuition across the gulf that separates us, by exceptionally gifted individuals." (22.60)
Here's our starting point. As the novel continues, this idea will evolve and change. We'll give you one guess as to who the "gifted individual" will be.
"And by 'love' He didn't mean namby-pamby old-maid love that's scared to look up from a hymn book for fear of seeing a temptation of the flesh. If God hated flesh, why did He make so much of it? God is no sissy." (27.116)
Pat disagrees with the idea that God sees sex and sexual desire as something that should be hidden and shameful. For her and the other Fosterites, sex is celebrated in a more open way than in more conservative religious ideals.
"In the twentieth century (Terran Christian Era) nowhere on Earth was sex so vigorously suppressed [than in America]—and nowhere was there such a deep interest in it." (27.121)
It's that old adage. If you make something forbidden or scarce, people are just going to want it more. In this future, this hasn't changed one bit.
"Exhibitionism" had been to her just a technical term—a weakness she held in contempt. Now, in digging out her own and looking at it, she decided that either this form of narcissism was normal, or she was abnormal. But she didn't feel abnormal; she felt healthier than ever. […] Okay, if a healthy woman liked to be looked at, then it follows as the night the day that healthy men should like to look." (29.41-42)
Jill reconsiders healthy sexuality for women. By changing her view on how she feels being looked at, she also changes her view on whether or not it's healthy for men to look. Since Stranger was written by a man, the issue can get a little thorny here.
But she was amazed to find that her excitement increased as she looked through his eyes at other girls. (29.83)
Jill vicariously feels what it's like for a man to look at a desirable woman. Again, her conclusions may seem odd depending on your point of view. But we should consider that the idea of understanding is more central to this passage than the conclusions it draws.
"Jealousy is a disease, love is a healthy condition. The immature mind often mistakes one for the other, or assumes that the greater the love, the greater the jealousy—in fact, they're almost incompatible; one emotion hardly leaves room for the other." (33.57)
Jubal tells Ben one of the creeds of Mike's church. By removing jealousy, in this case sexual jealousy, Mike hopes to increase the love between all the people in his Nest. An interesting note: it was jealousy that led Mike to being stranded on Mars in the first place, right? So without jealousy, Mike would have never become a Martian.
"Ben, the ethics of sex is a thorny problem. Each of us is forced to grope for a solution he can live with—in the face of a preposterous unworkable and evil code of so-called 'Morals.' Most of us know the code is wrong, almost everybody breaks it. But we pay Danegeld by feeling guilty and giving lip service. Willy-nilly, the code rides us, dead and stinking, an albatross around the neck" (33.81).
Jubal argues that a moral rule everyone breaks can't be much of a rule, and if everyone breaks the rule, then why should anyone feel guilt for breaking it themselves? Or to quote Liam Neeson in Kinsey, "Everybody's sin is nobody's sin."
"Sex should be a means of happiness. Ben, the worst thing about sex is that we use it to hurt each other. It ought never to hurt; it should bring happiness, or at least, pleasure." (33.88)
Male-femaleness is the greatest gift we have—romantic physical love may be unique to this planet. If it is, the universe is a poorer place than it could be." (36.140).
Mike places the ability of two people to join together in sex as unique to the universe. Check out how male-female is joined into one word, suggesting the bridging of the gap mentioned in Quote 1.
"That's what a sexual union should be. But that's what I slowly grokked it rarely was. Instead it was indifference and acts mechanically performed and rape and seduction as a game no better than roulette but less honest and prostitution and celibacy by choice and by no choice and fear and guilt and hatred and violence and children brought up to think that sex was 'bad' and 'shameful' and 'animal' and something to be hidden and always distrusted. This lovely perfect thing, male-femaleness, turned upside down and inside out and made horrible" (36.144).
Whew. In short, Mike's philosophy and practice was meant to remove all the bad from the act of sex and the human spirit in general.