I might reread Friday to check-- it's a book about desperately searching for a home, and I suspect that an alert reader might find something fishy, even in the early descriptions, if only from their sketchiness. IIRC, Friday seems to love the atmosphere of the place rather than the individuals.

While we're on the subject, afaik no human society has anything like line marriages. On the face of it, they seem workable. Any theories about why they don't happen?

I actually haven't read Friday, I was just picking an example from the sci-fi canon more or less at random. There are plenty of other examples, too; I just meant to point out that sci-fi fans get more exposure to these kinds of ideas than most others.