You are correct - there is no mention of that in the Bill of Rights. However, in the Supreme Court’s interpretation of “Freedom to Speech”, they found that speech that incites violence is not protected, such as yelling ‘Fire’ in a crowded movie theater and patrons being injured trying to flee. Or if you are protesting that people should go blow up the Capitol building while it is in session, even if you personally have no plans to. There are limits to free speech.
And you are confusing the content contained in some books, such as rape, to an actual manual/how-to book for committing a felony. Even if rape isn’t viewed negatively in fictional works, it certainly wouldn’t be considered instructing someone how to safely rape another person. Greaves’ book does precisely that, only he is focusing on children instead of adults.