Conspiracy truthers recruitment booth on Tulgana IV
A conspiracy theory was a dubious theory about the true nature of an event. It might involve conspiring parties and cover-ups. Those who believed in conspiracy theories were sometimes known as "truthers". Sometimes, they displayed their theories on a conspiracy board. (LD: "Cupid's Errant Arrow", "Reflections")
In 2364, William T. Riker found Jean-Luc Picard's theory about a Starfleet Command takeover to not be credible. (TNG: "Conspiracy")
In 2376, Seven of Nine was briefly overcome by a conspiracy theory regarding Voyager's becoming marooned by the Caretaker. (VOY: "The Voyager Conspiracy")
Steve Levy believed in several conspiracy theories. While on a date with Beckett Mariner in 2379, he said that "Wolf 359 was an inside job." A year later, he still held this view, and also claimed that Changelings were not real, and that "the Dominion War didn’t happen." (LD: "No Small Parts")
A pair of conspiracy truthers set up a booth on Tulgana IV, and, believing they were being controlled by parasitic beings, heckled Mariner and Brad Boimler. In the midst of a meltdown caused by different hecklers destroying his rank pip, Boimler accused the two of being "pathetic gossipy weirdos" rather than genuine truth-seekers. (LD: "Reflections")
After the Attack on Mars in 2385, Raffi Musiker became consumed with conspiracy theories about how the synths were not responsible, leading to becoming estranged from her family. These theories featured the Conclave of Eight. (PIC: "Stardust City Rag")