My main point is that there is a major difference between use and abuse. Marijuana abuse is definately harmful, as far as I can tell. Responsible marijuana use is not.
Lots of things people do aren't conducive to long term gain in martial arts study, but as long as they think the tradeoff is fair, they're going to keep doing it. Playing PlayStation games certainly isn't conducive to long term gain in martial arts study, and neither is having a few drinks on saturday night. The fact that you don't personally enjoy it shouldn't affect the freedom of speech on this board.
(christ, I'm coming off as a huge [censored] here, sorry