One major positive of legalisation would be some control/listing of potency. Throughout the 60s, 70s, and 80s, the strength of cannabis sold was fairly similar across the board. Even skunk type weed was not generally as potent as it is today, in a market driven by young consumers who demand the strongest, smelliest product, the breeders of the seeds have aimed to please this dynamic. I would imagine that a legal, controlled market would be taxed on strength in the manner of alcohol - with a majority of users opting for 'beer' strength, rather than 'whisky', but unfortunately any smokers are stuck with what the market is offering.