I could replace your use of “cryptocurrency” here with “Pokémon cards” and nothing would change. Yet you don’t seem concerned with the buying, selling, trading, owning of Pokémon cards with regard to their utility. You are not the arbiter of utility. Nobody is. If you have no utility for digital cash, great. That doesn’t mean others don’t. You don’t have to play Pokémon if you don’t want to.