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

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.