When says you have to secure a single node? In silk road's wake, there are dummy sites popping up all over. But at the end of the day, it's just a communication problem, putting sellers with buyers over a secure channel. You don't need one millionaire and one website to do that. Just a distributed and secure communication network in which it's not worth the effort to track down each and every person involved.
If there is one takeaway for me from the latest round of revelations, it's just how much effort they are willing to expend. You're right about it being a communications problem. The possible solution of the child-sites popping up all needing to link buyers and sellers securely just sounds to me like you'd have the same issues with competency as one node, multiplied a few times. Encryption isn't easy for most users, and any sort of managed interface or network to make it easier is a huge point of failure potentially. Maybe encryption knowledge at a base level just isn't where it needs (for the population in general) to be for a distributed marketplace like that to work anytime soon.a distributed and secure communication network in which it's not worth the effort to track down each and every person involved.