Quote
“In fact, cash is likely a much more anonymous means of transferring value than virtual currencies. The ownership string for virtual currency is public, though not the actual owner name and address. If that name and address are at one point identified by law enforcers, law enforcers have a powerful mechanism to track entire chains of transfer of value, in a way that cash would never allow. The arguments used against virtual currency anonymity may thus be much weaker than comparable arguments against cash.”
Bitcoin always hits the headlines when some crime is committed where bitcoin was involved as a transfer of value yet crimes committed using fiat are hardly ever reported on. Most probably as bitcoin is a hot topic for news at the moment but it creates a skewed perception that it's the 'currency' of choice for criminal activity.