Bitcoin is simply a technology. As a technology, often the first use it finds is in the hands of criminals. The first cars were used as getaway vehicles. The first telephones were used to plot conspiracy. The first telegrams were used to run long-distance mail-fraud schemes and Ponzi schemes. The first forms of electricity were used to run medical hoaxes and scam people. These things always happen with a new technology, and they happen with bitcoin, too.
