If the first economic argument for legalization of marijuana (http://markostake.blogspot.com/2010/12/high-economics-part-1.html) didn't pursuade you, there are many more.
Incarceration for marijuana offenses is fairly small, accounting for less than 1% of the prison population, but it does still keep about 60,000 inmates supported at taxpayer expense. It is believed that the annual cost is on the order of $1.2 billion. That does not include scarce court time, legal resources or police time which is allocated to enforcing an unpopular and needless code of law.
Then there is the medical aspect. Marijuana is now used to treat nausea from chemotherapy, anxiety, pain, glaucoma and insomnia. But is it safe? Remarkably so. Of all the causes of death monitored by the Food and Drug Administration, marijuana comes in DEAD LAST, with NO fatalities (http://www.economicsjunkie.com/annual-drug-related-deaths-in-the-us-marijuana-ranks-last-with-zero/).
Even aspirin, which many doctor recommend be taken daily, accounts for thousands of deaths per year.
But, despite overwhelming societal and economic benefits, Proposition 19 did NOT pass in California. What are the arguments against? The main objections to legalization are focused on the belief that marijuana use is addictive, a "gateway" to more serious drugs and a factor in greater crime. There also exists the fear that once legalized, we'd become a nation of Cheech and Chongs.
The U.S. Drug Enforcement Agency (DEA) has issued this position piece outling the arguments against: http://www.justice.gov/dea/ongoing/legalization.html.
The addiction argument is absurd in light of legal alcohol, cigarettes, soft drinks and prescription drugs, all of which are far more injurious to the user and most importantly, can be FATAL to abusers and second-parties. Caffeine is addictive. And, to some, so is shopping, sex and gambling. So is reading "Marko's Take"!
The crime argument is equally absurd. Marijuana is a sedative. How many stoners pull off a bank heist or hold up a 7-11? And, should marijuana become legal, the price would certainly drop. So, the notion that one has to go rob a gas station for a few joints becomes preposterous.
According to federal statistics, nearly 100 million Americans, or 1/3 or the population, have, at least at one point in their lives, imbibed. Cigarette smokers make up about 25% of the adult population, while drinkers make up more than half. Experience with both prohibition and other countries experimenting with legalization have shown that very few NEW people will become users. And, so what if they do?