Here is the SEC's definition of a Ponzi scheme:

"A Ponzi scheme is an investment scam that involves the payment of purported returns to existing investors from funds contributed by new investors. Ponzi scheme organizers often solicit new investors by promising to invest funds in opportunities claimed to generate high returns with little or no risk."

And they have even a paper out on it for "virtual currencies": https://www.sec.gov/files/ia_virtualcurrencies.pdf

Hence, crypto operates pretty much like a Ponzi scheme. Most of all, since there is no inherent value to extract in the event of a price collapse to zero.

You are also apparently not terribly informed about the biggest Ponzi scheme in US history: Bernard Madoff. And he was a one-time chairman of that marketplace called the NASDAQ. N.B.: Some people were able to recover some portions of their investments because there was both Madoff's wealth and the small amount of still valuable securities.

I take it your accounting experience has not been terribly involved with markets or regulators.

This is to help you understand what a "marketplace" is, as well: a "marketplace" is simply where 2 or more people come together and do an exchange. You know, like the flea markets and securities markets, as well. And the weapons, drugs, crime-for-hire markets on the darkweb run entirely on crypto now. Yup. It is a bona fide marketplace.