I think this is brilliant. A very efficient way of policing and removing a lot of drugs from the market without spending a lot of public money and wasting time on the streets. Also the darknet is great as it reduces the violence associated with drug crime, by taking the drugs off the streets and into the legitimate courier business. You have to love technology sometimes.
How does that reduce the violence? Now the buyers have to go to the streets to get their drugs. Prohibition doesn't work. It creates much more violence than it solves.
It seems that you are actually agains policing it, which is not the way forward, as there is a large amount of the population which is against drugs, and their needs need to be accounted for by the Government. So by catering for both parties (users/dealers and police), the darknet is a viable solution that helps everybody in the end (efficient purchase, efficient policing, less violence, less waste).