In another thread I said, "Looking back I wish someone would have discouraged me as a teen from reading all the fantasy, horror, and science fiction and found me some better books." Pearldust asked, "What's wrong with fantasy? What's wrong with books like Harry Potter?"

The short answer: Nothing wrong with fantasy or any genre fiction, in moderation. The following is about reading too much of any genre, so if your reading is well-rounded, don't worry about what I'm about to say.

For one thing, most genre fiction is unoriginal and repetitive. It's an obvious irony that genres like fantasy and science fiction, in which anything can happen, are rigidly bound by convention. A few authors will pioneer a genre, your Chandlers, Tolkiens, Asimovs, Christies, etc., and they spawn a load of imitators who deviate from the forms the pioneers set only in details. How many independent cowboys, intuitive detectives, and crafty wizards does anybody really need? Once you've read the trend-setters there's not much need to read the imitators, other than to fill time that might be spent more profitably.

Again, reading a bit of fantasy isn't a bad thing, but too much of anything is. Reading exclusively science fiction and fantasy distracted me from other books I would've liked and should've read. I didn't get around to reading "The Catcher in the Rye", "To Kill a Mockingbird", Hemingway, etc., etc., until I was in my twenties. I was ready for them earlier but I was too busy reading books that were, to be frank, junk. I'm not saying that all genre novels are junk, but a large proportion is. By focusing so much on genres I increased my junk intake as I read more of the best authors' second-rate stuff and the second-raters' best stuff.

Which leads me to my next criticism of the form: much of it is unchallenging. Thinking back there weren't many books in the genres that made me think. Few tough questions were asked and solutions tended to be presented after the fact. While one could argue that certain genre novels and stories are based on problem solving, the problems in science fiction and mysteries are conventionalized and unrealistic. I suppose I could learn from Bilbo's problems, but the lessons are pretty obvious: don't give up, you gotta do what you gotta do, sometimes mercy is better than revenge. That's actually a pretty rich haul for a genre novel. I think all the really useful information I've netted from all the detective novels I've read is a couple pointers on rolling cigarettes. Books like, say, "Huck Finn", on the other hand, contain not only moral lessons but a picture of real life as people lived it, and I find it much more rewarding to return to Twain than to my favorite science fiction and fantasy authors. Most of my reading is for recreation, but that doesn't mean I shouldn't try for something a little tougher and hopefully a little more rewarding.

Even worse, genre fiction tends to be unenduring. In my old favorite genre, science fiction, even the originators are going unread more and more, let alone the imitators. In fact, some people claim the genre as a whole is dying off, failing to attract new readers. I feel safe in assuming that the current fantasy genre heavyweights, your Rowlings and Pratchetts will most likely see their readerships taper off as they are replaced by a new fad genre, probably within their lifetimes if they have reasonably long lives. More and more books of my favorite author as a youth, Robert A. Heinlein, are going out of print. What's more, his books haven't aged well for me personally and I was a big fan.

One unfortunate side effect of genre fiction's unchallenging nature is that I was unprepared for the demands of literature. For example, genre fiction never has been much for symbolism. If E.R. Burrough's hero John Carter says he's on Mars, he's on Mars. However, if Ernest Hemingway's hero Nick Adams says he's fishing, well, maybe he is just fishing and the story's OK if a bit pointless. Then again, maybe the author is telling the story of his youth, the river is a symbol, and if you pick up on that the story is much more than a simple fish story. Coming from a background of strict literal-mindedness didn't help me spot things like that and to this day fairly obvious symbols in books and films pass by me unnoticed. If I'd started sooner I might be doing better.

Unoriginal, inferior, unchallenging, uninformative, short-lived, and literal-minded-- these things don't apply to all genre fiction, but do apply to a great deal of it. Some of the other charges leveled at fantasy, science fiction, horror, westerns, and mysteries-- chiefly the charge of escapism-- don't hold as much weight for me. While a bit of fantasy (or mystery, or science fiction, or whatever) is fine, reading exclusively or primarily genre fiction is, in my opinion, a mistake for a young reader. Or an old one.

I was going to present a well reasoned, subtle antithesis to your post ironikinit. However, a sober and mature reconsideration of the facts has led me to a more Catholic defence of genre fiction:

"RECANT OR DIE HERETIC!"

I had a tendancy as a teen to fall, HARD, for a genre, or an author, and read nothing else for six months or so. In retrospect, I think that this was no bad thing. It was only by exploring the genre thoroughly that I was able to see past the conventions, all the bells and whistles, and understand why the best in the field truly were the best. If I hadn't read so many detective stories, I don't think that I would appreciate just how good Nero Wolfe really is.
That said, I must agree that much genre fiction is formulaic and unchallenging. Unfortunately, I think that this is what the fans like about it. I remember, when I was about 14, and going through a historical romance period - adults would say how wonderful it was that I was reading instead of watching TV, but I would think to myself that there was really not much to choose between the two. Reading is not necessarily more stimulating and thought-provoking than television.
My son is now almost 14, and is heavily into fantasy and science fiction. My main concern with this is that the video games he plays (his other great passion) are also very fantasy - based, and it's just too much of the one thing. I'm dealing with this by encouraging at least some other reading, and by steering his fantasy reading towards the best of the genre, rather than just indiscriminate gulping. One problem with fantasy specifically, as compared to other genres, is the sheer length of the books. A trilogy in which each book is over 600 pages is not at all unusual. A person just needs to come up for air after reading one of those. It means a considerable investment in time and mental energy, no less for a mediocre book than for a good one.
So, on the whole, I think my attitude, and my advice, is - go ahead, dive deep, really get to know a genre, but then climb out, shake yourself off, and dive into a different pool, and explore it.