I don't know how the system in the United States works, here in the Northern Territory of Australia a cannabis user can escape being arrested for possessing small amounts (eg less than 50 grams of plant material). If found in possession of cannabis in such quantities, authorities have the option of siezing the cannabis and issuing a $210 fine.
Here in the Territory, there is a great drug and alcohol problem. The drug of choice at the moment is probably alcohol closely followed by cannabis. There is plenty of evidence to show that cannabis destroys lives and families just as well as alcohol in the cities as well as in the smaller communities. For example, alcohol fuelled crime and violence is exceptionally bad, but in the Territory, frequently the crime and violence is cannabis and alcohol fuelled which is just beyond belief. People are quite happy to spend the majority of their earnings on cannabis and alcohol, neglecting basic necessities such as food for themselves and frequently their kids. (another example, a deal bag may cost about $50 in town, in a community that same deal bag could go for as much as $200)
Drug and alcohol programs don't seem to work effectively and community leaders don't have enough influence over young people anymore.
Cannabis may be just a plant, and so is opium, but the negative effects on the community as a whole vastly outway in percieved benefit gained from getting high. Prohibition has been shown repeatedly to be ineffective, people will always find a way to get what they want, look at how effective alcohol prohibition was. I do believe that governments are cheating themselves out of tax dollars by not regulating cannabis, but I certainly don't believe cannabis is a good thing or even a harmless thing.
There seems to be plenty of studies out there to support either argument, that cannabis is harmless, doesn't cause lung cancer or is harmful, has just as much chance to cause lung cancer as cigarette smoking and increases the chance of mental illness in users. I agree with the mental illness, I've seen far too much of it to believe it's a mere coincidence.
The laws here in the Territory appear to be fair at the moment, users get a lesser penalty to suppliers. The main thing that changes the severity of the sentence is that frequently there are other offences attached to the drug use.