Fincher was speaking to the Telegraph about his new film Mank, which is currently in cinemas and is also being released on Netflix next month.
But as well as his forthcoming biographical drama - which centres on screenwriter Herman J. Mankiewicz and his battles with Orson Welles over screenplay credit for Citizen Kane - the topic of another film cropped up.
Fincher compared Joaquin Phoenix's central character in Joker with Travis Bickle from Taxi Driver and Rupert Pupkin from The King of Comedy, both films by Martin Scorsese, arguing that the former is something of a mashup of the other two.
He said: "I don't think anyone would have looked at that material and thought, 'Yeah, let's take Travis Bickle and Rupert Pupkinand conflate them, then trap him in a betrayal of the mentally ill, and trot it out for a billion dollars'."
Responding to the headline on social media, many people agreed with Fincher, with one tweeting: "David Fincher said that Joker is a betrayal to the mentally ill and that is fact. Thanks Dave. Screw Joker."
Some others have argued that his words may have been taken out of context, arguing that the 'betrayal of the mentally ill' is actually referring to society's betrayal, in the context of the movie.
One person said: "I think people are taking David Fincher's quote out of context. Is seems like he's saying society's betrayal of the mentally ill rather than the movie's betrayal."
Elsewhere in the interview, Fincher also compared Joker with other, psychologically dark films - attributing some of its success to Christopher Nolan's 2008 Batman sequel.
"Nobody would have thought they had a shot at a giant hit with Joker had The Dark Knight not been as massive as it was," he said.
Fincher also reflected on his own experiences with 1999's Fight Club, which starred Edward Norton and Brad Pitt, in relation to Joker.
"I'm sure that Warner Bros thought at a certain price, and with the right cast, and with De Niro coming along for the ride, it would be a possible double or triple," he said.
"But I cannot imagine that movie would have been released had it been 1999."
He added: "The general view afterwards among the studio types was, 'Our careers are over.' The fact we got that film made in 1999 is still, to my mind, a miracle."
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