Would you consider someone sick who writes short stories about violence/insanity/rape and other dark themes?
If you do, you condemn a huge chunk of world literature. Stories are full of dark themes, from the Greek myths to Shakespeare (I rate macBeth as the greatest horror story ever written) to nursery rhymes. Yes, nursery rhymes. Little Red Riding Hood’s granny gets eaten by a wolf; Hansel and Gretel cook a witch in her own oven; Snow White eats a poisoned apple etc – and these are stories considered fit for the youngest children. And remember that for every author who writes dark tales, there are thousands that read them for enjoyment.
Well, I suppose that not all stories can be about care bears holding hands as they cross the rainbow of joy to feed their unicorns. Sometimes the care bears also have to take part in orgies and commit multiple homicides. I personally would rather read about the mean care bears. I don’t know about you.