A little bit of erotic worldbuilding

What immediately comes to my mind is religion. One reason why even discussing sex openly is looked down upon (in America at least) is that we were founded by Puritans, and many of those puritanical morals have been absorbed into our society. Even in the modern "bible belt" of America the morality of sex without marriage is still fairly taboo. So, if in your setting the religion (or lack thereof) denotes that casual sex is awesome instead of evil... Well, there you go!

What about one of these exclusive, luxury, anything goes European clubs? Places like The Box or some of those supposedly wild places in Amsterdam?

I've played with this idea but couldn't pull it off. No Pun intended.

In many of my stories the acquisition of sex is a primary goal or motivation for the main character.

First you gets the sugar, then you gets the power, then you gets the women.

If you jump straight to the sex, removing the tension, conflict drama, emotion, and even uncertainty that it will happen, what remains is the mechanics of a penis traversing a vagina and it doesn't take many pages for that to get old.

In porn, if the performers aren't groping within the first sixty seconds you hit fast forward. The set up isn't important, so when you begin to analyse a society with unfettered promiscuity, the cultural social and moral questions that arise are more interesting than the sex.

It could just be the way the culture developed.

Look at our culture; we are very accepting of violence. Sure you cant just walk up and punch someone in the face, but they have public boxing and wrestling which children are permitted and sometimes encouraged to attend.

You can violently kill someone and show blood and guts etc. in an R rated film (that's 18+ in Australia) but you cant show an erect penis ejaculating.

In our society sex is taboo, in yours it might not be.

I guess your society could be one that was as accepting of sex as it was of violence. Perhaps it's moral roots came from a religion that was very sexual? Maybe something like the "Kama sutra" is their bible?