Not legalize, DECRIMINALIZE! There is a difference.
Why decriminalize rather than legalize? If you are going to let people possess it, why not take billions of dollars out of the hand of organized crime by allowing for legal production and sales through legal channels similar to the way we do with alcohol. That would be a huge blow to organized crime. They'd lose billions and billions of dollars every year. A legal industry would crate a lot of jobs for law abiding tax paying citizens, and we could raise more than enough in sales taxes and excises to pay for all the costs of regulating the new legal industry. Aside from all the jobs created and revenue generated as an added bonus people who buy marijuana from licensed facilities wouldn't be offered drugs like cocaine and Ecstasy from their dealers like we see happening today. The clerk at the “pot store” wouldn't be any more likely than the clerk at a liquor store to offer customers cocaine or meth or any other illegal drugs. With decriminalization you basically allow people to smoke it, but you don't separate marijuana from the harder more dangerous drugs. You don't deliver a major blow to organized crime by taking a multibillion dollar business from them and depriving them of the massive distribution networks for marijuana that they currently use to distribute the much more dangerous drugs like heroin and meth for which there is far less demand than marijuana. You don't stop people from selling a dangerous product with poisonous insecticides or other chemicals on it. If we're going to decriminalize, we might as well go all the way and legalize it and regulate it similar to the way we regulate alcohol.