I just noticed this thread and would like to put my two cents in.
There's some things about MJ I find problematic. Firstly is that it's airborne. A mind altering drug that that can reach me without my consent I find intrusive. I find tobacco smoke similarly irritating not for the brain altering part but for the lung altering aspect. I feel that other people should have the right to damage themselves but not me.
Then there's the thing where embryos can supposedly be damaged in the womb by pot. Have their brains changed on them. Not cool.
And lastly there's the thing about people being impaired while driving and there is currently no level/test for that.
Overall though I feel pot is likely less troublesome than alcohol so by extension probably should be legalized and the risks minimized as much as possible. I'd also like to advocate for SOMA, that sci-fi drug of yesteryore that causes a nice high without causing any damage http://www.denofgeek.com/other/12573/top-10-sci-fi-drugs
There are lots of things related to both cannabis and hevyer drugs that are more than problematic.
Occasional recreational use of marijuana shouldn't be more of a problem than a glass or two of a good wine at dinner. Those two glasses are good for you, but for many people they aren't enough. And that makes alcohol a social problem even if it doesn't make you
aggressive and even if you
realize that you shouldn't drive when intoxicated.
That, however, is not what this thread is about. The question is: has prohibition worked? When it comes to alcohol, it was determined a long time ago that it didn't work, either in the US or in my country. People didn't drink less. The only positive result was that bootleggers got rich.
Now some people (like NoIBnds) see the negative effects of drug use, and common sense tells them that if marijuana and hard drugs are legalized, those effects will be ten times worse.
But will they? Is common sense to be trusted? If prohibition of alcohol taught us anything it was that prohibition itself creates more problems than whatever you are trying to prohibit. And there is some evidence that this is true about the war against drugs too.
Legalizing drugs does not solve most drug-related problems, but at least it would move the drug trade from the gangsters to people who can be controlled. And most probably you wouldn't see an increase in drug use.
I suppose that passive pot smoking could be a problem, but hardly much more difficult to handle than passive tobacco smoking.
And when it comes to marijuana: cannabis does have medical uses and some of the potential ones haven't been studied because of this ridiculous taboo.