If somebody were to sell a book or documentation about something illegal and show you how to do it such as a blackhat method at whatever price, would the seller of that book be doing something illegal?
I can't speak for any country but the U.S., but generally it is not illegal to sell a "how to" book about a subject just because the subject itself is illegal. For example, you can buy books on how to grow a certain illegal plant, how to fool drug tests or how to build a silencer. There are exceptions (such as distributing bomb-making instructions if those instructions are intended to assist in the actual building and use of such a device) but generally it is considered a right of free speech guaranteed under the Constitution of the United States.
Yes. I agree with Attorney. It's alright to sell books that appears to have an illegal content. I have read a book from one author giving tips on how to die quickly. Though in my opinion, these kinds of books should be regulated and banned if possible. These can be dangerous for the teenagers who still don't know what's real and what's not. Let's not talk about freedom. Freedom can be destructive for people who does not know how to use it.
It is legal in the country where there's freedom of speech. But this doesn't mean that authorities will not look into you and what you do. So you'd better be clean.
This line of thinking can be equally as dangerous. Who's to decide what's right or what's "safe" for another person to have or use? It could easily set up a situation where controlling people could limit the options other people have because "it's in their own best interest." Plus, if that was the case, people wouldn't be allowed to drink or smoke anymore. There's risks there. It damages your health. If that's the case, they're not using their freedom right and it should be banned. See? Dangerous.