You won't have to traverse dark alley ways to buy impure product trafficked from far away lands. Instead you will sit in your basement bio lab with elemental components and code together the necessary little functionality that you wish to have your host of living beasties produce for you. From heroine to vanilla, oil to alcohol.... when every one can bio synthesize what ever they want from scratch ...what need for outside suppliers?
Drug dealing will go extinct and in it's
place will spring up a wide industry where templates for production of all kinds of inebriating or mind dulling agents will emerge....the same way maker 3D files are shared online for use in 3D printers...or modeling files are shared for rendering CGI.
As people will be able to clandestinely supply their own drugs the risk of trying to buy them illegally doesn't have to be taken nor will there be a desire to deal as you would simply share your biobug blueprints with who ever asks so that they can create their own living factories of what ever wonder their little minds can code up.
Decriminalizing all manner of drugs today has seen strong positive results in all the places it has been tried without exception. The correct path is to enable people to get access to the vice of their addiction so long as it is safe and clean and then treat their addiction. It works for alcohol...it works for cigarettes and it will work for all the other drugs (even heroine!!) and beyond the fact that this is the best way to deal with the drug underworld is the fact that soon there will be no way to stop drug production at the grass roots level once people are coding and creating their own biobugs that can make them for them.