From what I've read of some of the most compelling editor-writer relationships in history, and from what little I've experienced for literary magazines, editors aren't merely devoted word-crunchers for the writer. They have their own agendas, and in fact, to be great editors they've got to have an independent vision and artistic sensibility. A creative writing professor of mine spoke to my class about how editing was itself an art, and that some people were born to be great editors just as some were born to be great writers.
At first I found it hard to believe -- can an art ever be refining and honing someone else's creation rather than creating something yourself? But the more I thought about it, the more I started to believe it. After all, many visual artists create art by using ordinary objects or scenes and making us see them in new ways by bringing them into a different focus.
After the jump: so who's in charge?
Other editors didn't even consult with their writers before making changes that dramatically altered the way a work might be read. This is particularly evident in the nineteenth century, and in countries such as Russia where censorship was always rearing its ugly head. To keep their jobs, editors had to walk a line of balancing art with acceptability. In this way, great works of Dostoevsky and Tolstoy were changed forever.
So is the editor king? It seems to me that in a "healthy" writer-editor relationship, an editor needs to take a strong hand, but a writer must always have inviolable veto privileges for any suggestions of the editor. I've seen how a weak editor can hurt a book; the more respected a writer gets, the more delicately and reverently his work will be treated, and writers such as Stephen King and Philip Roth could have used someone who was tiptoeing around them less, I believe.
With regard to your own work, if you get an editor looking at it, be sure to have a strong sense of your story. If you can hang on to that, you'll be able to defend your work and fight off any disastrous changes. At the same time, remember the old proverb about the flexible willow sapling that bends in the storm and survives while the old oak is broken. Be flexible, and be willing to see another person's interpretation of your own work! If you're lucky enough to work with a great editor, your work will reach its true potential in his or her hands.