Marijuana is currently classified as a dangerous narcotic under Federal law. This despite the fact that marijuana is no more dangerous (arguably less dangerous) than the legal drugs tobacco and alcohol.
Legalizing marijuana for recreational use would allow the FDA to regulate its safety and potency; would allow the Treasury to tax the sales, distribution, etc; would free up law enforcement resources to pursue dangerous criminals, and would shift control this multi-billion-dollar cash crop from criminal organizations to regulated farmers and industries: we can create a new taxable industry overnight, create jobs, reduce crime, spur investment and keep otherwise law-abiding citizens out of prison.