People can (and have) said the same thing about gold for thousands of years. The evidence is in, cryptocurrency is some sort of asset. It is unclear how big the crypto market is, but at this point it seems a safe bet after the last decade that there there is enough interest to sustain a billion dollar market in cryptocurrency even under the most pessimistic of scenarios. It is probably going to be quite a bit bigger.

The next real question is how to value it. That'll take a recession to figure out by clearing out the scams, but it'll become clear in time.