The first is to educate the people we introduce to BitCoin about the ways in which it is similar to cash in that it can be used illegally, but the majority of it's use is for legitimate purposes.
That's the defence that was used for p2p file sharing when it first emerged. People said it could be used legitimately and shouldn't be restricted just because of the illegitimate users. I think Bitcoin probably has more legitimate uses than Napster did (for example) which counts in its favour, but I think there'll be difficulty persuading the public at large that Bitcoin is legitimate especially when the media will undoubtably be whipping up a storm about Bitcoin being used for drug pushers and child pornographers.