Article in the Houston Chronicle.
"I feel that the ending of book four is frightening, but there are reasons for that. I was dealing with an evil character," Rowling explained. "I do not see, in five, six and seven, that I have to, kind of, up the stakes with every book at all. I wouldn't necessarily say that five is going to be darker. But I couldn't promise that there isn't more sad stuff coming."
"It's a short-sighted thing. It is very hard to portray goodness without showing what the reverse is. That's always been my feeling about literature," Rowling said. "You find magic, witchcraft and all those things throughout children's literature. Are you going to stop The Wizard of Oz? Are you going to stop C.S. Lewis? At what point are you going to say these are dangerous and damaging?"
J.K. Rowling has the future mapped out for Harry Potter