In my opinion this is not quite true, because there's a basic form of "investment" scheme going on. People exchange value (money, energy) for some kind of token

In my opinion this is not quite true, because there's a basic form of "investment" scheme going on. People exchange value (money, energy) for some kind of token, expecting to get some value back. They may actually be satisfied with getting only a fraction back in many cases (money laundering...). Cryptocurrencies do have some non-scam value because they fulfill the technical end of such a belief based value store. Don't get me wrong. Plenty of scams in that business...