Mostly books of the mid-late 1960s. I’m thinking *The Left Hand of Darkness* (1968) and *Memoirs of a Spacewoman* (1962) but there are many others from this time period specifically.
Most of them regard it as a sort of alternative world custom that is either only taboo for those from Earth or an old taboo from prior (20th) centuries. Did people think this was going to happen, or was there generally a sexual shift around this time that I don’t have context for?
by Helloitsme61