Criminals use cash much more often than BTC, I think. But the myth of using BTC by such people is a good reason for BTC haters to vote for ban of cryptocurrencies.
Bitcoin may not be yet so much popular in criminal and it is also not so much easy to use it. in fact they will never take the risk on something that they not easily understand. On other hand I think it is the responsibility of the state control the criminal activities of the people therefore I do not think that we can blaim bitcoin for criminal activities.