> gold has a source of revenue besides the investors; namely, the purchases by consumers like jewelers and industry, who take gold out of the market (2/3 of the production) for uses other than re-sale. When one buys 1 oz of gold, one gets a chip of a metal that one can sell to those consumers, and thus obtain some money that does not come from other investors.

Yet we didn't conclude only from this all crypto is a ponzi.

That all crypto is a scam clearly comes from the fact it is a negative sum game. When you have a game where you can tell which set of players in total are going to lose and which set of players in total are going to win without knowing the rules of the game -- that's clearly a scam. All you need here is any commodity with baked in transaction fees. The exact same would be true if you traded with plastic poker chips but you needed to pay someone a fee whenever you bought or sold one. Indeed, reviewing the process with such chips makes it more clear, stripped of high tech mumbo jumbo.

Stolfi argues all crypto is a Ponzi because 1) people invest into it because they expect good profits, and 2) that expectation is sustained by such profits being paid to those who choose to cash out. However, 3) there is no external source of revenue for those payoffs. Instead, 4) the payoffs come entirely from new investment money, 5) while the operators take away a portion of this money. Our argument in the previous section was 3-5, you need to add 1 and 2 for it to become a Ponzi. https://ic.unicamp.br/~stolfi/bitcoin/2020-12-31-bitcoin-pon...