Ian:
Great letter! I agree that the "stop campaigning for bitcoin's destruction" message might backfire, and the message should be "we're an innocent bystander here." You might even offer to help law enforcement better understand bitcoin so they can develop tools and techniques to catch criminals who use it.
I've been thinking of how to react to this story, and am tempted to appeal to people's greed/fear with a message of "your country may miss out on a huge new opportunity and be left behind if you try to stamp out innovative new technologies like bitcoin."