Treefarn, where are you residing?
While I don't agree with trim's arguments, I disagree with the statement that marijuana is more dangerous than alcohol. It's useless to say that it's not dangerous, because it carries with it inherent risks. It impairs co-ordination, and smoke inhaled from a joint carries four times the tar of a cigarette.
Increasing age has nothing to do with exposure... I would say the adolescent population has a much higher exposure to the drug and weed culture than does middle aged persons. Invictus probably has a decent amount of experience with alcohol despite that he's "only" 19. Most teenagers in the States start drinking significantly below the legal drinking age.
I will say that weed is a social drug, it fosters camaraderie just as well as alcohol and does not turn you into an anti-social hermit that pisses their life away. Contrary to certain other drugs, such as Salvia or Heroin, weed is highly social. Perhaps the perception is different in America where weed is frowned upon more and there is probably a smaller population of weed smokers, but I would say that the weed smokers here in Canada smoke much more responsibly than anyone drinks responsibly.
I will say that I've noticed that drunk driving seems to be a larger problem among American adolescents... of course, this is anecdotal evidence, but all my American friends do not seem to think that driving drunk is a huge deal. They recognize the risks, but they often do it anyways, to my dismay, and it seems every time someone in one of my friend's school's dies it's because of drunk driving. Here in Canada, nobody I know would ever drive while drunk. They find the notion absolutely absurd, as if it was a straight ticket to trouble (which it often is). Despite that I know more people in Canada than I do in America and both groups of friends come from similar socioeconomic backgrounds I find the incidence of drunken driving is much higher in America.