Then I would leave it up to each individual state as to whether they want to allow the sale of it or not.
This mirrors my opinion exactly (although I'm a Canuck, not American). Decriminilization has the dual benefit of leaving people alone who indulge in the privacy of their homes or wherever else it's deemed acceptable, but still giving authorities the power to take a person off the street who may be so stoned as to pose a potential danger to themselves or others. The basic message becomes "Don't get in someone else's face with it, don't be a mush head in public, stay out of your car and for crying out loud don't give it to kids or we'll screw your thumbs to the wall." Before long the street trade would dry up as people replaced their friendly suppliers with hydroponic gardens, etc.
The trick will be to lift the criminal penalties without turning our cities into open air dope markets. This will then leave the cops the ability to go after hard drug dealers and importers, and hopefully provide help (society, not the cops) for those unfortunates who are wrecking their lives through addiction. Just MHO.