Considering even the psychiatric community has a hard time nailing down what a psychopath is beyond "someone detatched from reality", I'd imagine that mindset is probably straight alien for most people. Also, something you should probably be made aware of, where it concerns mental disorders, there isn't a "psychotic disorder", there is rather a family of disorders in the psychosis family. Such as: Sociopaths, Schizophrenics, Dissociative Identity Disorder, et cetera. Some are milder than others, and individual cases can typically range from "manageable" to "institutionalized vegetable."
Playing a dark culture would be significantly easier. Add in any form of mass dehumanization and you're done; such as slavery, involuntary human sacrifices, or other violations of basic human rights.
Hope that proved educational.