Drug dealers are the biggest and most widespread gateway drugs, "why not try a bit of this now Jonny?"
I find that for most people even if they don't think of it that way, alcohol is probably their gateway drug.
Very few people who don't drink that I know use drugs, apart from some hardcore MJ only people.
I hear what you say, I can only smoke weed when either alone or with benzos or booze, else I get all paranoid. Not cripplingly so I just go quiet and withdrawn.