i'm kind of on the fence with this issue, though i do lean toward decriminalisation rather than straight out legalisation.
in my opinion, marijuana is a "gateway" drug purely because of the contacts people come into contact with when using marijuana.
lately here in NZ, more people have been using methamphetamine (or P as it's called here). every single person i have met that does P (and i have met a LOT), has been introduced to it by their marijuana dealer.
in EVERY case, they got given a free sample of this "amazing new" stuff that the dealer had just gotten, with the pure intention of getting them addicted, and sadly enough, it worked.
i have these people waste away because of their addiction, and a few of them are now dead.
marijuana on the other hand, is relatively non toxic when compared to other drugs, and there have never been any deaths due to overdose because of marijuana.
compared to such things as cigarettes and alcohol, it seems kind of idiotic for them to be legal, whereas marijuana, which is much less of a danger, is still illegal