Legalize, tax and control just as with tobacco and alcohol.
- significant reduction of law enforcement costs, court costs as well as incarceration costs and all of the administrative costs that support these activities (working in government I can assure you that these costs are extremely high. Keeping someone in jail for a year is what $70k? $80k? The salary of the cop, the cost of the police station, the cop cars, equipment, the salary of the judge, court clerk, the building maintenance etc).
- increase in economic output via the growth of a new industry (or one that is legitimized, at least) and the reduction of people who have a criminal record for a trivial offence (try getting any good job with a criminal record, many employers perform background checks and will discard you the minute something comes up!).
- increased revenue for all levels of government through taxation.
- increase in personal freedom (the libertarian in me absolutely loves this).
- significantly reduced income for criminal organizations and reduction of criminal activity overall.
- increase in quality control and dosage of the product through standardization and regulation.
Very few negative side effects have been demonstrated consistently in any studies. It's completely unregulated and the entire industry is run by criminal organizations.
A vast majority of people who smoke weed are "functional" stoners, that is they go to work five days a week, they pay their bills, they pay their taxes and do not otherwise break the law. They smoke their joint like you enjoy having a few beers at home after work on Fridays.
I smoked for a little while a few years ago, almost daily at one point and it just lost its appeal for me after some time. I haven't smoked in years so I don't have a dog in this fight. But I can say with certainty that anyone strongly opposed to legalization has never really tried the drug in the right context.
It makes you a bit lazy, a bit hungry and puts you in a different state of mind for a few hours. It's not addictive, it doesn't turn you into a zombie (not anymore than you can get wasted on alcohol) and if everyone was high in he world there would be no war, no violence, but there would be a significant shortage of frozen burritos
The time has come to take our heads out of our asses, give ourselves that extra little bit of freedom as a society, that little bit more cash in our collective pockets and legalize the damn thing.