"This is a book full of things that I believe to be true. It therefore belongs in non-fiction" - random nutjob with a blog

In real libraries, they only stocked published books, and publishers decided what to publish. So the publishers acted as gatekeepers and fact-checkers (sometimes not so well, as the Howard Hughes example shows), and the library could accept their classification.

Now, anyone can write a book and add it to our hypothetical library. If the librarians aren't going to classify the books, then who does? Because someone has got to...