Someone else earlier said...

Rating: 9/10 (4 November 2019)

...that "this film is a study in psychology".
Well, he was right. But it so much more. It's also blunt criticism towards our healthcare systems all around the world, our dumb and incompetent politicians don't care about and don't invest in psychiatric care. They just want to bury and lock away the Frankenstein monsters they're responsible most of the time in creating in our societies.
Personally I don't concider myself a full blown Frankenstein monster, never been on the wrong side of the law ever, but that doesn't mean I don't emphasize with Fleck's inner turmoil. Get ridiculed and beaten mentally or physically too many times and that person will change. Period.
This film is brilliantly portrayed by Phoenix. But it's apparently not brilliantly received by some viewers.. leave your worries for it being an inspiration for 'in real life' violence, instead view it as a bold way to get our corrupt politicians' attention - to take psychiatric care more seriously once and for all! More funding nation/worldwide and professionally done with a more humane approach.
And oh, once and for all - quit taking medieval scripture and theologians seriously concerning questions on morality and ethics. Evil isn't born. It's made. And always has been.
(P.S. I have always loathed DC comics. However, The Joker may be the only interesting character they've ever created)