Move fast and break things — our mantra in Facebook's early days — was an appropriate slogan for a college social network. It's not appropriate for the global monetary system.

This week, Facebook and 27 other partners announced a plan for a new digital currency called Libra that could be used to send money around the world. If things go according to plan, some of the world's largest corporations will oversee this new currency, through an independent association based in Switzerland that has a membership fee of $10m.

If even modestly successful, Libra would hand over much of the