There's something special about documentaries -- you can convince the audience of practically anything if you're a good enough director.

My favorite case is the Errol Morris documentary Mr. Death. It follows the story of a man who went from an electric chair technician to a holocaust denier. Morris attempted to direct the movie from the subject's perspective so that the audience could understand how you could slowly become a holocaust denier.

When he showed the movie to a Harvard film class, half the class believed that Morris himself was a holocaust denier, and the other half of the class believed the subject's (holocaust denying) side of the story, specifically that the Auschwitz gas chambers never actually had poison gas in them.

https://en.wikipedia.org/wiki/Mr._Death:_The_Rise_and_Fall_o...