I have a very clear idea of how to deal with stuff like that. Which is:
You can express whatever opinion you have about whatever. Including the fact that you like something, or WISH to do something.
What you can’t do, is to make a PROPAGANDA about things that are illegal. In other words, influence other people to commit a crime. I’m not completely sure how people deal with that in other countries, maybe is the same way we deal with it here in Brazil, I honestly don’t know. But anyway, here in Brazil we have a term called “apologia ao crime” that would mean something like “apology for crime” that refers to that. As I said, maybe you guys have similar stuff there with another name. And well, I searched for it and find nothing. But whatever.
The idea is: You can’t encourage people to commit ANY crime, that is illegal. But you can say your opinions about it.
So, in an example, a KKK video is a no-no here, since it’s INCENTIVE people to be racists. But a simple comment on it, even if you say you agree with it, is not a crime, because that is your opinion. But of course, the context of everything you say must be taken into account.
So in your example. What that “paedophile manual” says?
He is commenting on things that criminal pedophiles do? Maybe even saying a positive opinion of the author about it? That would be Ok for me.
Does it try to teach people how to molest children? It would say that teaching to do a crime, if not in the context of trying to find ways to prevent it. That would be an incentive to it, so is an “apologia ao crime” and so it’s illegal.
Also, trying to be more clear:
“I wish more people will rape children” → Opinion, so Ok. But I won’t recommend people saying that, since, that could be considered an incentive in some contexts.
“More people should rape children” → That’s an incentive, then not Ok. And again, doing like me here, and saying that as an example. That’s also OK. As I said, depends on the context.