Crypo cannot create or destroy fiat currency. So if you sell your crypto and make a profit in dollars, it's exactly because someone else bought it at a higher price than you did.
And they expect someone else will buy it from them, in just the same way...
So every dollar that comes out of cryptocurrency is because a later investor put a dollar in.
Doesn't that sound like the definition of a Ponzi scheme?
The core of the coin ecosystem are the stable coins, which are generally pegged to fiat, but are only backed by fractional reserves of cash. So the same USD can be recycled many times to buy Bitcoin.
Not only that, but the stable coin operators are under no obligation to exchange their coins back to you for the pegged currency at face value.
Tether is essentially an unregulated bank with nominal deposits totaling 73 billion USD, no obligation to pay depositors, a huge amount of minimally disclosed liabilities, and unaudited financial reserves.
Ponzi was but an amateur.
>but are only backed by fractional reserves of cash.
Maybe tether, but that isn't true of all, or even most stablecoins. Some stablecoins are overcollateralized rather than fractionally lent. As for the obligation, USDC for example is a fully audited system (by firm Grant Horton, who performs weekly audits), backed 1:1 by cash/cash equivalents and redeemable for $1 USD.
https://coinmarketcap.com/view/stablecoin/
However, even USDC is still doing fractional reserve banking because an unspecified amount of its reserves are tied up in securities that have maturities up to 90 days, so they are still susceptible to a bank run. Though, granted they seem to be running a much more respectable operation than Tether.
The third biggest stable coin BUSD, looks pretty shady as well. They release monthly audited accounts (good), but they're terse as hell. What liabilities do they have? Have these reserves been used as collateral in loans? Which banks are they in? What steps have the firm taken to audit these funds? No way to know, we're just get a terse list of aggregate numbers.
In the gold market, you are buying a contract to deliver you physical gold at a point in time.
Similarly with tulips, Beanie babies, fine art, and old watches the underlying asset is what it is.
MLMs and other traditional pyramid schemes also do typically hand you real assets, and so are not inherently Ponzi schemes.
But when that extrinsic demand is driven by fraudulent claims (like Madoff's "beat the market every year" returns), then it can be considered a Ponzi scheme, because they don't even get the tulips or Picassos or whatever, they get nothing.
The gray area, especially with MLMs, is what kind of support and service benefits you get - these are often fraudulent or misleading (Ponzi scheme) but they don't inherently have to be.