Some borrow little more than the names of Ms. Rowling's characters, lifting plots from other well-known authors, like J. R. R. Tolkien, or placing the famously British protagonist in plots lifted from well-known kung-fu epics and introducing new characters from Chinese literary classics like ''Journey to the West.''The funny thing is, nothing has really changed in that regard. Journey to the West itself borrows from so much. Take, for example, the scene where Sun Wukong hides in Pigsy's marital bed, pretending to be his wife and then beating him up (this is before they become fellow travelers, of course). There is a scene just like it in the Water Margin--and surely countless other tales lost to the ages.
There were also a lot of "fake" sequels to the classic Ming and Qing novels. There was the Later Journey to the West, for example, in which Sun Wukong's descendant and others of a later generation go to the West once again. There is also A Supplement to the Journey to the West, which actually is supposed to be a dream that Sun Wukong had during the course of the "original" story that went unrecorded. There are also sequels to the Water Margin, in one of which several characters from the Water Margin escape to create a Utopia in "Siam," which actually seems to be a fictionalized Taiwan. There are tons of revisionist sequels to Dream of the Red Mansion, written by people dissatisfied with the ending. (Fan fiction from Late Imperial China?)
Surely some (if not most) of these are hack work, but at least some of them surely have something to say. I wonder, if a book--even a work of fiction--is saying something you don't agree with and you want to engage the argument on its own terms, isn't writing such a "fake" sequel a natural move? Can your ideas be "fake" just because you aren't the initiator of the conversation but the responder or objector?
A writer named Alice Randall got swept up in that question when she "re-wrote" Gone with the Wind from the perspective of a slave in a novel called Wind Done Gone. She got taken to court for copyright infringement and eventually won the right to engage Gone with the Wind on its own, fictional, terms by calling it an "unauthorized parody." The Wikipedia entry for the novel notes that it is "parody in the broad legal sense: a work that comments or criticizes a prior work" despite the fact that "the book is not a comedy, as the term 'parody' would imply in its common usage."
The NY Times article also mentions that unscrupulous underground publishers snatch up these "fake" Harry Potter books and publish them without paying royalties to the authors. This has been going on since the Ming Dynasty as well--see my post about Li Yu, the author of the Carnal Prayer Mat, complaining about piracy.
Update: The Times now has synopses and (very) brief translations of selections from a few of these "fakes."