Marijuana should be removed from the criminal justice system and regulated in a manner similar to alcohol and tobacco.
Legalizing and regulating marijuana will bring the nation's largest cash crop under the rule of law, creating jobs and economic opportunities in the formal economy instead of the illicit market. Scarce law enforcement resources that could be better used to protect public safety would be preserved while reducing corrections and court costs. State and local governments would acquire significant new sources of tax revenue from regulating marijuana sales.

(http://www.drugpolicy.org/marijuana-legalization-and-regulation)

Revenue boost: As state and local governments struggle with rising costs and decreased revenue, many are looking for creative ways to increase income to pay for everything from road repairs to new parks. Some believe that marijuana legalization could be a windfall in the form of new taxes applied to its distribution and sale. In Colorado, for example, analysts suggest that taxing the drug could raise between $5 and $22 million annually.

More effective law enforcement and criminal justice: Many advocates for legalization note that by decriminalizing the substance, police officers will have more time and money to pursue criminals for other crimes, including those involving violence. They also argue it would create wiggle room in the criminal justice system, allowing prosecutors and judges to focus on violent crimes while freeing space in crowded prisons. One study estimates that nationwide marijuana legalization would save governments $8.7 billion each year.

Less money supporting organized crime: Legalizing recreational weed cuts off an important revenue stream for many in the illegal drug trade. Advocates of legalization contend that by making the substance less profitable for criminals, it will decrease the violence associated with the trade. The result could save lives while taking pressure off of law enforcement.

Safety controls: When a person buys marijuana off the street, there’s no way to know exactly what dangerous substances are cut into the drug. While current legalization efforts don’t directly address safety issues, they do create a framework for a safety control system, which would work to eliminate some of the risk that comes from smoking a substance potentially laced with toxic ingredients.

Wider access for medicinal use: Some people from inside and outside the medical community argue that the drug is an effective treatment for a range of conditions, including epilepsy, Crohn’s disease, posttraumatic stress disorder (PTSD), and multiple sclerosis (MS). In more than a dozen states, including California, Massachusetts, and New Jersey, medical marijuana use is already legal under certain guidelines. The decriminalization of weed would allow more people to use the drug for its believed health benefits.

(http://www.drugrehab.us/news/pros-cons-legalizing-recreational-marijuana/)