I'd argue that by legalizing pot, you can tax it. Tax the growers, the sellers, the buyers. It'll more than make up for the revenue lost in fines for possession. It would decrease the jail population. It would allow police to focus their attention to other crimes. It would be more readily available to those who might benefit from the medical side.
Some argue the danger to society or personal health. So, let's legalize it, but make it an aggravating factor for criminal violations, like drunk driving. It does impair judgment and affect reaction time, so let's treat it like drinking.