I am of mixed opinion on the issue. To me it is like a Pandora's box. Legalization is likely not going to be a complete solution to a problem. It may lead to easing some current societal pressures but it may lead to other unintended / unforeseen issues.
As for cost / benefit - as previous posters have stated, that is also uncertain - we may move the cost equation around but I feel that there still we societal costs. Will the costs be more or less bearable than now - I don't think anyone really knows. Having people in prison for minor indiscretion also does not seem right. so perhaps I may be slightly for legalization. Basically you can't legislate morality. Everyone has a world view and level of moral persuasion with which to make a choice. Hopefully parents, friends and persons of influence will provide adequate guidance during formative years so that you make more right than wrong choices.
As for misuse, that is going to be a continual human failing. The medical profession brought us oxycontin. As intended it probably was a good thing for those in unbearable pain and whose life situation was imminently terminal. However the docs here in Canada started handing it out like candy. I think this was just to shut up whinny patients. My mother got hooked on this stuff - it made her addicted with all the addiction problems starting to show up. So now she is hooked - oxycontin now cannot be dispensed in Canada but they have some other substitute which she takes - maybe not as bad as the oxy but still seems to me addictive. So I guess this is a long winded way of saying even the experts fail at responsible handling. Perhaps if my mother was prescribed med marijuana she would have stopped whining and sucked it up, as she had no condition that causes unbearable levels of pain but periods of some discomfort. Now she is hooked and the docs and drug companies are happy.
When they build the regs and rules maybe they should allow you to grow it in your garden as well. Why should the companies in the government circle be given a legal cartel / monopoly. Note that I could grow grapes / fruit and make my own wine or beer if I chose and do it legally.
