The phrase "conspiracy theorist" gets thrown around these days like pies get thrown around in an episode of The Three Stooges. It has become so overused in fact that it almost doesn't mean anything anymore (and has been superseded by the "fake news" psyop as a means of discrediting truly independent media that criticizes the establishment or asks too many questions).
Once upon a time, being a conspiracy theorist wasn't automatically akin to being a crazy tin foil hatter. That all changed swiftly after John F. Kennedy's assassination, when polls showed nearly half the country was not buying the Warren Commission's findings or its report solidifying the government's official version of events; a Gallup poll reported in January 1967 that at least 46% of the country did not believe Oswald acted alone. (Bear in mind this was a full decade before the House Select Committee on Assassinations investigated JFK's murder and concluded that, "Scientific acoustical evidence establishes a high probability that two gunmen fired at President John F. Kennedy," and that "President John F. Kennedy was probably assassinated as a result of a conspiracy.")
At the same time, Mark Lane had just released his book "Rush to Judgment: A Critique of the Warren Commission's Inquiry into the Murders of President John F. Kennedy, Officer J. D. Tippit and Lee Harvey Oswald" and a three-judge panel had just ruled that District Attorney Jim Garrison had enough evidence to take Clay Shaw to trial on charges of conspiring to assassinate JFK.
The Central Intelligence Agency released the following memo in April 1967 categorized as "PSYCH" which essentially weaponized the use of the label "conspiracy theorist" and laid out a number of dirty tactics using "elite friendly contacts" including politicians and media figures to discredit and shut down any claims and ultimately demonize anyone who attempted to challenge the government's official version of events.