For years, crypto skeptics have asked, What is this for? And for years, boosters have struggled to offer up a satisfactory answer. They argue that the blockchain—the technology upon which cryptocurrencies and other such applications are built—is itself a genius technological invention, an elegant mechanism for documenting ownership online and fostering digital community. Or they say that it is a foundation on which to build and fund a third, hyperfinancialized iteration of the internet where you don’t need human intermediaries to buy a cartoon image of an ape for $3.4 million.

Then there are the currencies themselves: bitcoin and ether and the endless series of memecoins and start-up tokens. These are largely volatile, speculative…