Depends how you define 'biggest time stealers' - tv and video games are huge time stealers for many people. And the fact that drugs have a chemical effect on the brain does not mean they are necessarily worse than, say, watching some braindead tv show while stuffing your face with fast food, or sitting in a classroom for hours listening to a monotone voice regurgitate some dull bullshit you don't care about. Many people have had beneficial experiences with drugs, for example Steve Jobs with LSD.