Eh, I think in the long run that will be more of a hindrance than a help, as it will give governments in many places a plausible reason to attempt to ban or limit its use (which would tend to lead to a vicious cycle of only criminals--however you define that--using it).

On a more practical level, I can't remember a time my credit card has been refused for local or international transactions (and any additional fees are largely invisible to me, the consumer). Paying with a credit card also carries certain advantages: If the goods aren't delivered, I spend 2 minutes on the phone and get my money back.

For the vast majority of consumers, the headache of converting local currency to BtC, learning how to use it, and finding a reliable escrow service will greatly outweigh the benefits of being able to buy drugs (especially as states decriminalize drugs). That keeps BtC firmly in the grasp of speculators.