Bitcoin and other cryptocurrencies are uselessFor blockchains, the jury is still out AN OLD saying holds that markets are ruled by either greed or fear. Greed once governed cryptocurrencies. The price of Bitcoin, the best-known, rose from about $900 in December 2016 to $19,000 a year later. Recently, fear has been in charge. Bitcoin’s price has fallen back to around $7,000; the prices of other cry