I honestly don't think the proponents of legalization have thought this through completely. Their idea of what the reality of legalization would be is likely very different from what it would actually be like.
I don't believe they realize just how good they have it now and just how radically different things will become with government regulation.
They bitch about the prices now, wait until they see what taxation will take that to.
They enjoy the convenient availability of scoring a bag of weed off their friendly neighborhood pot dealer, their friend next door, down the street, etc. That will no longer be the case. Joe Dealer will be out of the market without a license and face heavy penalties for bootlegging if caught.
They envision the whole pot culture as it is staying as it is, without the bust factor of course. It won't be like growing tomatoes in the back yard with anyone and everyone being able to do as they please. The government will take a dim view of that sort of thing, the same way as an illicit moonshine still will put you in the big house for hard time.
No, it would not be a free for all Utokia. You will be able to purchase it but that will be from Philip Morris with a big fat tax stamp on it. Doubt this? Go look up big tobacco/marijuana and you will find this has all been laid in place for years in anticipation of legalization.
Be careful what you wish for, you just might get it.