...promiscuous sex, but it's normal? They all live in these giant towers called "Urban Agnon's" and life is perfect, but then someone escapes, and it gets hectic. I read it a few years ago, and can't figure out what it's called or who the author was.
If we are thinking of the same book, I read it years ago as well. It's "The World Inside" by Robert Silverberg. I studied it in university, along with Stranger in a Strange Land on how politics/attitudes of the sixties stretched into speculative fiction. The link below takes you to a plot description.