i know tons, hell my weed dealer got better grades in college than i did and he smoked grams of the shit a day. hell most recreational drug users i know are much smarter and more interesting people than all the quaint, straight laced old farts sitting on their high horses talking about how "drugs are bad kids" while they drink their beer and smoke their cigs.
i really think we need some perspective. no substance is "evil", it's what people do with it. it's all propaganda. plus i don't really think it's that hard to classify yourself as "functional", hell i'd even go so far as to say that most drug users are functional. people always think of this image of junkies living on the street sharing needles, but those people are more the minority. it's true that drugs can have a negative effect on one's life but most people catch themselves before they hit rock bottom, imo.