I think it is, like most things in that cat., as bad as you let it be. Its one thing to just play an RPG, another to be obsessed with it. If you do it in moderation and don't become obsessed with it, I don't see a problem with it. If it becomes all you think about... then you might want to start to worry.
reason why a lot of people seem to hate mmorpgs is that people have lost everything to them. people have become so obsessed with mmorpgs that there lives have fallen apart. but people have let stuff less then a video game destroy there lives.