Ah, but you could never quite be sure of that. There would always be that tiny suspicion in the back of your mind, and that is the seed from which your paranoia would grow. And the fact that everyone around you is mentally whispering to one another would also be disconcerting.
That kind of paranoia isn't normal in the Federation.
The Betazoids seem like an open and friendly people. They've presumably been Federation members for quite awhile as of TNG. I see absolutely no reason to distrust them or to assume that they would ever monitor anyone's thoughts without permission. They just don't seem like the type who would do that.
I mean, Deanna doesn't go around reading her crewmates' minds, does she? And remember the trial in "The Drumhead", which had a full Betazoid as the prosecuting attorney. Theoretically he could have just read Simon Tarses' mind and been done with it. But he didn't...
In any case, visitors to Betazed are presumably aware of the natives' natural telepathy, so anyone who is that afraid of being eavesdropped on (no matter how unjustified that fear is), won't bother going there in the first place.
It's like the Deltans. Sex is part of every aspect of their culture. Yet if Ilia was any indication (and I'm sure she was), then Deltans "would never take advantage of a sexually immature species". So it's probably the same story here - Betazoids would never impose themselves on a
mentally immature species.
Although with the Deltans, there's the added complication of their pheromones being so strong (IIRC, because of this, visitors aren't allowed on Delta itself - only its outer moons), and not even Deltans themselves have any control over that.
(Ilia said she took an oath of celibacy but I'm not aware of any measures she took to inhibit her natural pheromones. It was obviously affecting Sulu and Chekov...)
Are there any books, Trek or otherwise, that contain an in depth speculation about what a telepathic society would be like?
Not in Trek, no.