In a note titled “I come to bury Bitcoin, not to praise it,” Paul Donovan, UBS bank’s wealth management global chief economist, took the opportunity on Tuesday to predict that Bitcoin is not just an economic bubble, but one that has begun to burst. Looking at a drop in value from near $20,000 at the end of 2017 to as low as $3,200 last week, the longtime cryptocurrency skeptic felt confident enough to say: “The cryptocurrency bubble may be in its death throes. A loss of over 80% is not healthy. Economists said from the start that Bitcoin and the like would never be currencies. They never will be currencies.…