> I don't think "one flew over the cuckoo's nest" romanticizes mental illness, for me it is about demonizing institutionalization.
Intent is one thing, effect is another. One Flew Over the Cuckoo's Nest, the book and movie, broke ground upon its release, but one of its secondary effects was to establish the mid-20th-century mental hospital as a gothic setting, akin to the ancient stone manors of old, full of terrible secrets -- not to mention bizarre characters -- that are ripe for literary exploration. Today it's been almost completely tropified, especially since in the current era Great Literature is by definition introspectively psychological. An easy way to establish that your play or movie is "arty" is to set it in such an institution. One of the weirdest instances of this was in The Great Gatsby (2013), which wholly took place in a mental hospital (the plot of the novel being Nick's recollections to his psychiatrist) and implied that Nick admired Gatsby almost to the point of a crush and was so devastated by his death as to need psychiatric attention.
I do recommend you read One Flew Over the Cuckoo's Nest, the novel. It is written from the perspective of Chief Bromden, and his mental illness helps intensify the themes of subtle control, exercised by tyrannical people and institutions, with specific delusions he has that make him sensitive to that control.