Who says only the government can make money? This year the value of the private currency bitcoin has climbed to unprecedented levels, while at the same time becoming far less volatile than in previous periods of rapidly increasing demand. Bitcoin has reached these new benchmarks despite news that might have depressed its value, such as the Securities and Exchange Commission’s rejection of a fund permitting small traders to invest in bitcoin on the stock market.

The SEC action prompted obituaries, but bitcoin is thriving. A...