I also have a dislike for punishing someone for the acts of someone else. If someone who commits a crime, just so happens to have a particular book, it doesn't mean all the owners of that particular book should be punished for their transgressions.
It's an unpleasant form of collective punishment. And it means that all of them have to suffer for something which has nothing to do with them.
Fictional stories and images on the internet have no relationship with reality. There are no victims, there is no one harmed. You don't have to like the content, that is fine, but there is no good argument about bad morals or government intervention unless you're proving actual harm.