While I can emphasize a bit (I used to play WoW, but "grew away from it" and now spend a large portion of my time in search and rescue and musical performance), I have to say that this is a very judgmental POV to take. You're seriously going to compare playing WoW to smoking? Even in the worst case, at least playing WoW is a step up from watching some inane TV show with no interaction. It's not like anybody suffers from second-hand MMORPG.
And you can always play moral superior: instead of reading a book, why don't they start their own company? Instead of going for a walk, why don't they run a marathon? Hell, I could see how someone could look down on the activities I choose ("why rescue idiots who got themselves into trouble? Let natural selection sort it out!" or "why perform music that's already been performed thousands of times before by better performers?"), but FFS, sometimes "wasting time" is some of the best time well spent.