once you cede your argument in any way (say, with fictional incest) fascists have their foot in the door.
once you cede that one kind of fiction is evil, fascists will take that same logic and apply it to everything else.
this is "think of the children" pearl clutching about trans and queer folk, D&D, video games, etc etc etc. it's weaponized fascism and you're falling for it by moralizing fiction and policing thoughts.
this doesn't mean you can have personal taste or triggers, that we shouldn't age-restrict things, tag them with warnings, or think critically about how we (individuals and society) ingest media. that doesn't mean disregarding the fact that fiction can affect reality.
it just means acknowledging the fact that you can't know a person's thoughts. all fiction can be harmless and good for something, for someone, somewhere. instead of letting fear and disgust drive your reaction, flex that empathy and sympathy and reconcile that there are minds out there that you don't understand--and that doesn't make them evil.