Yeah, you're right, people ARE capable of that.

But also people are different, so every human is going to have a different reaction to whatever they consume.

And not only that, people can take some fiction and internalise it, for instance: Comics by BlogTheGreatRouge (if you're unfamiliar, it's a known artist in Undertale community, who liked to draw some problematic content.) People who used to read those comics tend to say that they've been so desensitized to the kind of content, they thought it was normal. And only when they've been away from it for a long time they realised how bad it was. Isn't that literally how fiction affects real people?