Without even looking further, I knew that the most likely front-runner would be Sword of Shannara, with honorable mention going to Atlas Shrugged and probably others such as Starship Troopers, some half-joking, half-serious nominations of Lord of the Rings, and so on. I posted a response to the topic which I felt merited a repost and more in-depth discussion; I quote it here:
I think "damage" is a silly idea. I predicted -- without looking at any of the answers -- what the front-runners would be, and whatta ya know, I was right. Had you not specified "Book", of course I would predict one of the front-runners would be "Star Wars" and possibly "Star Trek".
Yet without many of the "damaging" books, the field would be much smaller, much less popular, and much less likely to support *ANY* given author. Pick your favorite current authors; likelihood is that if you eliminated the top contenders in this thread, at least one or two of your favorites wouldn't be in print today.
The question is similar to the rants I see, quite often, on the anime newsgroups -- and that I've heard in person, too. The HardCore Fan of "The Good Stuff" bemoans the influence of X, Y, or Z on their industry. "Look at all the terrible Pokemon clones, etc..." And indeed, lots of trash (for whatever value of "trash" you may prefer) is produced.
But that burst in popularity ALSO finances all the GOOD stuff, makes it more available, promotes the overall industry. SO WHAT if lots of "trash" is produced? No one makes you read it, watch it, whatever. But all that money flying around allows more of the stuff you DO like to be produced, too.
You REALLY want to know what I think "damages" an entertainment industry -- SF/F books, movies, etc.? Anything that takes the FUN out of it. Anything that clearly reduces your fanbase. Of *COURSE* 90% of the new stuff inspired by ANYTHING will be drek. And if you don't like the original inspiration, you'll be even more certain it's a destructive influence. But when the actual EFFECT of the "drek" is to bring more money into the industry, finance more people -- including some of the ones you end up liking -- and most importantly draw in MORE POTENTIAL FANS of your chosen subgenre -- it's HELPING you. It's CONSTRUCTIVE.
I have no doubt that the answers on a similar question on movies and TV would have had, as one of the top contenders, "Star Wars". Which was responsible, almost single-handedly, for making the SF/F genre even vaguely acceptable to the mainstream.
In actuality, I don't think ANY type of book/movie, in itself, damages the subgenre, if it's at all reasonably well done -- and none of the candidates mentioned in the prior post were NOT reasonably well done. They may not be something the people dismissing them LIKED, but they were all at the least serviceable and at the most excellent examples of, well, what the author was trying to accomplish.
What REALLY damages the industry? Smacking around the fans (see MPAA, RIAA, etc.), treating the fans OR authors like idiots, or in other ways making it appear that the industry -- whatever the industry is -- doesn't actually care about the people who support it on either end. Books and movies are products. Some people will like just about any product. A product that appeals to a LOT of people has at least one thing going for it: a far greater chance that it will bring in at least a few people who will like whatever it is that YOU like.
* Quote from "Doctor Strangelove", as General Jack D. Ripper is explaining why he's going to start an atomic war -- to stop the insidious infiltration of the "International Communist Conspiracy" into the American Way of Life. A classic example of Overkill.
** For those unfamiliar with the legend, it is said that Eris, Goddess of Discord, became peeved one day when she was not invited to join the other deities of Greece on Olympus; so she popped in and dropped a Golden Apple into the midst of the others, with "For the Fairest" written on it. It of course caused no end of argument and squabbling, as all the other goddesses presumed THEY had to be The Fairest. This shows, of course, that James knew, and gleefully anticipated, the potential flamage that provocative question might generate.