Offline there is: - competition via violence - political narcoterrorism - profit maximization by product dilution - profit maximization by product deception (most street MDMA is amphetamine+nBOME mixture)
Online there is: - competition via quality, price (violence impossible in anonymous marketplace) - political separation via anonymity - drastically reduced product dilution (people do reviews with sources like ecstasydata.org) - drastically reduced product deception (see "The LSD Avengers" for example)
When you contrast these aspects you see that the online marketplaces do operate like a free market with the biggest difference being the incentives associated with deceptive vending. I think thats valuable just because it provides a real world simulation for what variables of legalization would look like without forcing any one country to take the initial plunge by themselves.