Should people write fantasy about things they're passionate about?
Should people write fantasy that includes controversial issues (abuse, incest, slavery, rape, torture)?
Should people write fantasy that takes the political issues of our own world and plops them down, thinly disguised, in another?
This last is what I call "message fantasy," where the author would really be better off writing a pamphlet or an essay but for some reason has decided to write a fantasy novel instead. The story is not the important thing; nor are the characters, or the language, or the setting, vital though that last is to convince your readers that they are reading a book set in another world. The important thing is the author's soapbox, and she is determined to tell you about each and every permutation of her ideas.
Let's examine the results of such a "message" on each of these things in turn, shall we?
Plot. Plot in fantasy is a tricky thing. It can sometimes be streamlined into simplicity, such as the Quest or the War, since fantasy is so close to archetype and has inherited the devices and trappings of older genres in which plot was generally expected to be more straightforward. But if your whole story is really like that, then you have major problems. If the reader can predict everything your charactes will do and say from the first page to the last, your problems are worse. And if the reason the reader can predict your story is because your characters are all focused on feminism, or religion, or saving the environment, or promoting family problems, then you shouldn't be writing fantasy.
Characters. Some people might argue that not all stories need to be character-driven. I would probably argue that, though with the corollary that I think the best ones are character-driven. (If they aren't, the plot and the setting had better be pretty damn strong, as in Tolkien; Middle-Earth carries the story as a setting, far more than most of the characters do). Message fantasy doesn't really care about the characters, though, because all of them are there to act as mouthpieces for the author- and prove the superiority of her values- or as mouthpieces for the opposition- and prove how much they suck. Characters become flat and shallow, recognizable at a glance: the Evil Chauvinist, the Heroic Woman Who Stands Up to Men, the Horrible Evil Environment-Destroyer, the Home-Wrecking Feminist, the Good Wiccan Woman, and so forth and so on. The characters are not fallible people with limited points of view, who might try the best they can but still not see the whole picture; they are perfectly right or perfectly wrong. Everything is black or white, in pursuit of the author's ideal. It's quite fun for the author, and presumably for those who agree with her, but it's death to any depth of character.
Language. Fantasy's language, just like its setting, has great power and great fragility at once. You are free to use many kinds of words that would sound silly if you spoke them aloud in a modern setting- but, simultaneously, you have to cut out many words that would fit in a modern setting and not an older one. Message fantasy does not respect the distinction. It is my opinion that many message fantasists do not even understand it. Talking about women's rights or the sacred feminine or the vaginal orgasm is useless in a world where the history has not included those concepts. If the author has built a world that includes those concepts, chances are that it is identical to the real world, and not a true fantasy anyway (see below).
Setting. Fantasy is set in another world, even those fantasies that take place on Earth, since they include concepts that most people would not accept seriously in the Earth that we know it. As Tolkien pointed out, one must know the difference between what does and does not exist, or one cannot write fantasy. Fantasy ultimately hangs on reason and truth and fact, depends on them strongly- to provide a sense of contrast to the world it sets up. A world that is exactly like our own except for those aspects that the author wishes to add to further her point, such as magic that destroys the environment, is a fake and false construct. A world that is supposedly other but includes the exact same political structures and struggles and messages as our own is likewise false. Embrace fantasy with your whole heart, or don't write it at all. What's the point of making your heroine have an evil husband and then discover that she's really a fighter for women's rights in a fantasy world whose history doesn't support that kind of thing? Why not set it in the real world, the one you're probably more familiar with anyway?
I am sick unto death of feminist fantasy, environmentalist fantasy, religious fantasy (both Christian and Wiccan), family rights fantasy, and any other fantasy that thinks the politics of our own world are more important than building something Other and Alive.