I'd think that the Harry Potter books are aimed more for children who are past the idea of straight forward good and evil. Besides I think that's clearly set out with Voldemort, ultimate evil (shown clearly in his aversion to love) and the good guys like Dumbledore. Therefore that leaves room for an ambiguous character like Snape. At the very least it's certainly made a long running conversation topic just trying to work out whether he is good or bad. I'd like to think that in the end he'll be a bit of both...I wouldn't want him to suddenly become this shining figure of niceness...although I doubt that would happen, the way he's acted in all the previous books! But what I mean is I wouldn't want some kind of soppy moment between him and Harry, after all these years of the fantastic tension between them both.