From the broad findings of the Bank for International Settlements, the Swiss-based "bank of central bankers" and the leading global authority on the crypto-craze (which I think of as just another cult):
"Cryptocurrencies have no intrinsic worth and are useless as a form of exchange. They entail exorbitant transaction costs. They are very slow. Together they have turned into an ecological fiasco.They are not backed by the assets and revenue streams of an established state. Most can be rendered worthless by fraud or digital manipulation. They are essentially Ponzi schemes that masquerade as citizen currencies beyond government control."