Here is an excerpt from this fine article by Chris Taylor at mashable.com.
The starting gun for the second wave of conspiracy entertainment was fired by Oliver Stone in 1991. JFK, Stone's expansive three-hour take on the Kennedy assassination, is a cinematic masterpiece. The editing, the tense John Williams soundtrack, the rollicking plot that carpet-bombs you with every hint of something amiss on that dark day in Dallas: Together, they leave you powerless to resist. I'm not the only moviegoer who left the theater thinking "well, something in that must be true."
You have to be something of an obsessive conspiracy theory researcher yourself to discover that much of the movie is fantasy. The real prosecution brought by Jim Garrison (Kevin Costner) relied on a witness whom Garrison had drugged and hypnotized; this witness is conveniently replaced in the film by Kevin Bacon's fictional prostitute (one of a number of aspects that make JFK look troublingly homophobic 30 years later).
The hits keep coming. David Ferrie (Joe Pesci) did not claim to be in the CIA and died of natural causes. The so-called "magic bullet" did not take the journey shown in the film, and more recent ballistics have come out in favor of its path. And worst of all, Colonel X, the whistleblower played by Donald Sutherland, was based on L. Fletcher Prouty — a professional conspiracy theorist, with ties to the far right, who advised Stone. Prouty published so many weird lies in his life that there are entire websites devoted to debunking "Proutyisms".
Even Stone himself admitted prior to its release that JFK was "not a true story per se." So what was it, then? A hybrid of infotainment and propaganda; one that boded ill for the future. To quote Stephen Colbert's parody conservative talk show host, JFK had "truthiness." It feels right that we don't know the whole truth about November 22, 1963. There is, as Eisenhower warned, a "military industrial complex" that benefits from vast Pentagon budgets. Kennedy was wobbly on the military advisers he'd sent to Vietnam, and LBJ was prepared to lie to ramp up U.S. involvement in the war (See: Gulf of Tonkin incident).
But none of that truthiness comes anywhere close to proving that LBJ headed up a vast shadow-state coup d'etat conspiracy — one that was simultaneously so efficient it erased all evidence of its existence, while also somehow relying on a bunch of colorful buffoons in New Orleans and Dallas.
And if you're prepared, like Stone, to make that huge logical leap based on Proutyisms? Well then, you might also believe that a larger, wilder conspiracy of baby-eaters has been able to cover up its existence for decades, and that only one brave anonymous soul in Washington is blowing the whistle. Colonel X was, in many ways, the forerunner of Q.