I have no doubt there are many books that most people would be better off not reading. That deplorable forgery,
The Protocols of the Learned Elders of Zion, would be an example.
I understand it is quite popular in parts of the Muslim world, etc.
But I wouldn't say
nobody should read it; there are those who have a legitimate, wholesome interest in the psychopathology of anti-Semitism, etc.
As for some other books that most people would be better off not reading, I suppose that labeling them as such would attract some people to pick them up and give them a try.
Some people have griped here about books they had to read, but I hope they can make a distinction between having been made to read something not to their taste or appropriate for the reading ability they had then attained, and thinking nobody should read them. Someone mentioned
War and Peace! I've read that several times, and it would be a keeper if I had to cut my personal library by 90%.
Happily, I don't remember that I was ever made to read a whole book that repelled me, bored me terribly, etc. Once, when I was a grad student, I had drawn up a list of books for an independent study in the classic British novel. I read a generous chunk of
Vanity Fair and asked the professor-tutor if I could be excused from continuing with it, and was allowed to drop it. I didn't hate it, but I felt that I probably had read enough of it to see the author's agenda, etc. But who knows, perhaps I will try it again sometime.