What happens if some eedjit reads a book of a similar story, and decides it's true, and kills themselves? Should the author be convicted of murder?
I see your point; however, in the case of Jehovah's Witnesses, their organization puts an arbitrary and unreasonable fundamentalist interpretation on the Bible by the governing body through their Watch Tower publications, which they purport to be coming from God’s one-and-only mouthpiece – but the destructive and dangerous aspect is that they use coercion and blackmail (disfellowshipping) through extreme undue influence.
In your example, a fiction or conspiracy theorist author wouldn’t be responsible for people’s deaths if they were to end up killing themselves or others – unless that same author deliberately held people captive, physically or even mentally, and used brain washing techniques based on fear and dishonest manipulation. Well, that would be another thing. Just think of the famous serial killer Charles Manson. He didn’t need to bother killing anyone himself – he was able to get his followers to do that himself!