OK, I’m going to come right out and say it:
Fiction does not affect reality.
Fiction affects people. And people affect reality.
Can fiction have an indirect effect on reality? Sure. But it’s not what’s responsible. People are the ones with moral agency. They are the ones responsible for what they do with the ideas they’ve been exposed to.
You want to defuse the harm you think a work of fiction can do? Target the links in the chain that actually matter:
Criticize bad ideas to change how they affect people. Don’t criticize with the aim of suppressing, criticize with the aim of discrediting. Censorship/silencing just keeps people from being exposed to ideas once, in a particular context, and leaves them unprepared when they encounter them elsewhere or come up with them themselves. A thorough rebuttal of a bad idea inoculates them against it and puts them on their guard next time they run into it.
Educate people about what aspects of a work of fiction would be harmful or dangerous in real life. If applicable, educate them on how to safely experience something similar. Don’t educate with the aim of killing their love of the fictional version–you will lose them, and it’s cruel and unnecessary. Educate with the aim of promoting understanding of how the fictional version does, and doesn’t, translate to reality.
Like. These are the underlying worries beneath “fiction affects reality,” aren’t they? Worry that someone will absorb messed-up ideas that aren’t adequately disclaimed/discredited in the text. Worry that someone will try to act out something that looks fun and exciting in fiction but is dangerous in real life. So cut out the middleman and go straight to the person whose choices affect reality. Don’t smack the book out of their hand, just tell them: I know you like that ship, but it’s okay if a similar RL relationship sets off all your alarm bells and leaves you scrambling for the exit. Because no matter how romantic the ship is, IRL that would be abuse.
Fiction needn’t be educational and fiction doesn’t always have clear-cut endorsements of who’s in the right. But the discussion that happens around fiction can include both.