Most of us like the dollar. It has lasted for centuries, survived two world wars, the Great Depression, and a siege by inflation. It works pretty well as a de facto global currency. Do we really need a purely digital alternative—one that isn’t backed by the Federal Reserve, lives only on a computer network, consumes vast quantities of electricity, and has no intrinsic value?

That profile describes Bitcoin, of course, and it is having a moment.

With…