yep, it's a fine mess indeed.
While it would be interesting to experiment with a society based on the "i have a right to do whatever i want to my body" quasi-Libertarian philosophy, that is not the case in the US. In fact, you dont, de facto, have a right to take your own life. Those who attempt suicide, but fail, are institutionalized to prevent further attempts. Is this Unfair? In some cases, sure. But, the history of "freedom" in the US is a history of tension between balancing the right of the individual to act freely and concern for the common good. At different political moments, policies are often made that weigh one more heavily than the other. For instance, the Patriot Act definitely sacrifices individual rights in favor of benefitting the common good -- i.e., preventing mass death and terror in the future. So in the case of marihuana, it has been so villified --deservedly or not-- such that at different moments over the past 70 years it has been deemed politically appropriate to outlaw the substance and restrict individual freedoms in the process. C'est la vie.
The rights angle as support for marijuana gets pretty tricky and can traverse a slippery slope for reasons Caine outlines.
I think the societal/medical, environmental, and economic benefits that marijuana offers are probably better platforms on which to rest the legalization argument. Most of all, I think it makes more sense to serve the common good by legalizing it and regulating it, just like gambling has been.
Moreoever, the presence of marihuana in the (informal) economy has never ceased. It's an important medicine and it is a popularly used recreational substance. And it could be a valuable renewable resource in the production of textiles and paper, and the oil from its seeds have many industrial and nutritional applications. For many reasons, the marihuana issue likely wont go away. Keeping it illegal does more harm to society than legalizing it. I understand that as a drug, it is abused by some folks, and has facilitated destructive relationships. But, part of that issue is psychological/biological--some individuals who abuse it would have abused another drug, marihuana is not the causal factor, but an enabler in this case. And part of the issue is social, since one has to turn to the black market to get marihuana, one can be (unnecessarily) exposed to behaviors that are violent and destructive (e.g., gangs). Legalizing it would help to address, much more directly and effectively, these social and psychological ills of the drug. For instance, if it were legal, finding and receiving help from a professional trained to assist you would be much easier and can be made affordable, that is insurance companies can cover treatment.
To be clear, I'm not advocating the tobacco and alcohol are legal so make pot legal too argument. That is more rhetoric than substance. I believe it sould be regulated like those drugs because marihuana use, like tobacco, gambling, and alcohol, will not go away. To the extent that it is abused, its negative effects can be mitigated if it were legalized and taxed based on user fees (e.g., only tobacco users pay tobacco taxes). And unlike tobacco, cannibas actually has some very productive and socially benefitial uses.
To sum what has become a very lengthy post, and I thank you for staying with me, I feel that criminalizing cannibas causes more harm to society than it supposedly prevents.