It a loop hole that they can use to fine you big time if you do not report your sales, is you sold weed, which if you did report you would be busted for selling. Kinda the same way they got al capone. They couldn't bust him for murder or anything to they got him for not paying taxes on the income. If they can't get you for selling then possesion with out a tax stamp is a fine and a crime.

Course it could always be leading towards legalization of cannabis. . . .