I have often wondered how the combination of the existence of telepathic races and privacy is handled in the Federation. As far as I know, Deanna isn't asking permission to the alien of the week to scan his feelings before she reveals to the captain that 'he's hiding something' or some such remark.
Now, in the case of Deanna, that might not be a problem, because people just very good at reading others (but no empathic abilities in the Betazoid sense) might arrive at just the same conclusion by reading very small clues that the person being read is unwillingly giving away but that elude others. We usually don't consider that a breach of privacy.
However, in the case of fully telepathic aliens I wonder where the borders lie of what is allowed and what isn't. (Had Deanna been fully telepathic like her mother, would it have been permissible for her to read the thoughts of the antagonist of the week they just met, without asking?)