"Of course not" is probably technically the correct answer right now. But, speaking as an American, we increasingly cannot assume the legal system to be logical. There is no "of course," there is only "ask a lawyer to find out what current practice probably is."

As a side note, of course, this is the very definition of the breakdown of law. But that is what the people want: a nation, not of laws, but of men.

What if the creator somehow profits from the system?

One could imagine a Bitcoin-esque system where the creator includes rules in the client that require every transaction to send a small cut to a Bitcoin address he owns. [1]

If that system then "happens" to be used for illegal purposes like drug trafficking, is the developer of the system committing a crime? It's distributed so he can't shut it down and he's no longer actively participating. What if he destroys the private key of the Bitcoin address?

It's an interesting thought experiment...

[1] Of course you'd need a critical mass of users and the right incentives to prevent people from starting their own "alt-markets" much like Bitcoin has spawned dozens of "alt-coins".

There's a real world example here, Liberty Reserve. Granted, it was centralized, but same law concepts apply. The problem with Liberty Reserve was not that they had a system used by criminals, but that they knew this fact and actively encouraged this activity to continue, including sending around lots of incriminating internal e-mails.