To begin, with Lewis Carroll: If you don't know where you are going, any road will get you there.
To continue, the question is, what your intent is in writing the story? What changes do you want to effect in the reader as they read the story?
A man has a dark side, characterized by demons. Perhaps the demons represent the notion that everyone has original sin (or words appropriate to a particular faith). Perhaps the demons represent the notion that modern life deadens our innate empathy. Perhaps the demons represent the notion that the existence of rock-and-roll/comics/Democrats/Republicans/thin-crust-pizzas corrupts the goodness of the individual. And so on and so on. Each of these possibilities requires a different colorization and texture for the demons.
I assume that once you describe the demons, you have thoughts about how the protagonist (and by extension, the readers) should respond and, thus, defeat the demons. Perhaps meditation, prayer, good works, tithing, or animal sacrifice are the answer. Maybe something else. More importantly, how you motivate the readers to adopt your "best practices." Describing a particular utopia in which the best practices are widespread sometimes works. But, for what it is worth, scaring the hell out of the worshipers (readers) is a time-honored tradition. Do it my way or suffer the pains of eternal fires (or bad hair days/endless cable news/bland frozen meals). Do I have your attention now?
So, the creepier, the better. But the responsible writer will ensure that there is a viable path out of the madness. No one wants to deal with a mob of folks all riled up with no clear place to go.