For instance, people claim that cryptocurrencies have real utility, and cite their use of moving money out of countries where traditional international currency transfer is difficult. While that is true, since the function of those transactions is to use the currency as a medium of exchange of other currencies it cannot explain the volatility of the exchange rate, as the current exchange rate is irrelevant if your purpose is simply to convert to and from other currencies.

The volatility is due to speculation, but without real utility it is difficult to see what anyone could be speculating on. One could say "belief that the value of the currency will continue to increase", but that's essentially admitting to it being a pyramid scheme. If people ever stop believing and refuse to buy, which would be easy to do since it is nothing to spin up another coin, the price collapses.

Now admittedly I am not an economist, so I make no claim to the correctness of my assessment other than that it makes sense to me. However, the vast majority of people pushing cryptocurrencies aren't economists either.