niknak,
The trouble with individual examples is that's all they are - individual examples. I used to know a chap who held down a well paid, responsible job, was never late for work even, seemed terribly normal...and he just happened to be a heroin addict. Does that make heroin OK? Of course not.
Personally I'm against the use of ANY drugs, legal or illegal, apparently innocuous or otherwise, if I'm going to be flying. The reason? It goes back to the day I took ibuprofen for a headache, went out with an instructor to practise auto-rotations, and my coordination at the level required had gone to pot (excuse the pun). And how long does alcohol, marijuana, painkillers, or anything else affect you? Who knows, really? It probably dpends a lot on your individual metabolism. Isn't it safer not to take anything?
Maybe the real question is: Why do any of us want or need to take any of these things?