Alcohol is an EXTREMELY dangerous drug. You need look no further than the problems occuring in our own backyard on Melbourne's streets to see the impact this substance can have on our society.
Which is why I can't fathom why Marijuana is deemed so dangerous. Unlike alcohol, you cannot comsume so much weed that you die - there has never been a recorded Marjiuana overdose in the world.
Marijuana doesn't contain the physically addictive ingredients of Ciggarettes (Nicotine). It is often smoked though water pipes / bongs - which means the temparature of smoke is lower and less harmful to your lungs. Using vaporisers made popular by medicinal marijuana smokers in the US, the risks are reduced further.
That said - it is potentially harmful if used irresponsibly. Eating fast food every day is harmful. Drinking alcohol every day is harmful. If you abuse Marijuana - that is you use it to excess - then it can be harmful. Which is why it needs to be regulated and people (especially kids who are most at risk) need to be educated about it.
Regulation will control any chemicals used in Hydro weed. It will allow the government to tax marijuana (Australia is one of the highest per-capita consumers of weed in the world) which will allow research and education into the plant.
Most importantly, it will reduce organised crime making profits from our nations most prolific illegal substance.
End the rediculous prohibition today.
Marijuana is an extremely dangerous drug - that is why it is banned. It is addictive, in an emotional if not physical sense. It is harmful to the lungs, and it is associated with a higher risk of psychosis and other mental issues. Its also incredibly dangerous to drive or operate machinery under the influence of Marijuana.
Of course, the exact same criticisms can be made of tobacco or alcohol, and you could certainly make a case that alcohol is 'worse'. So yeah, its a bit ridiculous that its still banned.
Do organised crime really profit that much from marijuana though? In my (very limited) experience, most of it just seemed to be grown in suburban backyards or hydroponic labs. Didn't really need the crime syndicate to get it organised because it was so freely available, unlike other drugs.
And this doesn't really answer the question about prohibition of harder drugs. Like it or not, illegality does help reduce use of things like heroin, cocaine and ecstacy. Maybe not amongst the hardcore users, but certainly amongst casual users (who may well become hardcore if its legal, given the addictiveness of heroin or cocaine). Education would help, I guess. I'm more worried about the kids though - like with alcohol today, what is restricted becomes something cool, a challenge to look forward too, leading to binge consumption when they finally get their hands on it.