Of course marijuana is a gateway drug. It's the first drug you try, and then realise that all the people who told you you were going to die or become a heroin addict if you were even in the same room as the stuff - didn't know what the hell they were talking about. As such, almost every piece of information given to you on illegal drugs becomes potentially false. That's a huge paradigm shift for anyone and it is the catalyst (the gateway) to seeking a more accurate representation of the "truth".
I can only speak for myself in this regard, marijuana was THE gateway drug for me because it was illegal and unsanctioned by government - alcohol was "safe" and legal. It was not a gateway drug (for me - that is, - no point dealing in absolutes)
If you're a parent, the worst thing you can do is paint an impractical picture of drugs to your child. We live in an age where they will find out that you were exaggerating (or wrong) and they will stop telling you anything about their life - because you are no longer to be trusted as a source of information - which renders your input absolutely useless. It is a fine line to walk with a kid, these days, because you might end up endorsing the use of drugs, too. I have no idea how I would deal with it, other than not bullshitting the kid.
Can't help if you're designated an "outsider mentality".
As for prohibition. E-Kul is right, but I think a generally grounded opinion on prohibition is a shrug of the shoulders. It is most definitely a restriction of our rights (those that have their own will) - but it is likely that the effects of lifting prohibition would be wide ranging and quite negative (for the idiots). I read people posting in my facebook feed of losing their car keys, finding them and then trying to tell themselves it was "god" who found their keys for them. These people do not even recognise their own capacity for choice so ahh, yeah, I'll shrug my shoulders on what is the lesser evil. If you're selfish, you're going to want prohibition lifted, but if you have a social conscience, I think you must agree that some of the idiots will not fare well under this new freedom (that's not to say it shouldn't happen - I just favour not picking a side).