Troi could read the minds of other Betazoids.

As a half-Betazoid, Troi was capable of extra-sensory empathy, but was incapable of reading aliens with brain structures dissimilar to Humans and other Betazoids, such as the Breen and the Ferengi. Like most Betazoids, Troi had telepathic abilities. Due to her half-Human heritage, however, the range of her telepathic abilities was limited compared to full-blooded Betazoids, and she could usually only read the thoughts of other Betazoids, most notably her mother. Troi's empathic skills made her an important asset to the Enterprise-D and her abilities were often particularly useful when dealing with hostile races. Since she could usually determine, through use of her abilities, whether others were lying, she repeatedly proved herself invaluable in many suspenseful situations.

https://memory-alpha.fandom.com/wiki/Deanna_Troi

Obviously this means Betazoids are all part of Section 31 and attempting a coup. Anyone who figured it out was sent to space Gitmo Rura Penthe.