Ask HN: Is Bitcoin really a Ponzi scheme?
For example, one requirement of a Ponzi scheme is that victims give their money to an individual or organization that then claims ( likely fraudulently ) to invest their money in such a way as to provide a high return. This allows the fraudulent party to disappear with the investor's money at any time - such as when too many investors demand their money back.
With Bitcoin, when someone buys a bitcoin, they actually receive delivery of the bitcoin. No one can take that bitcoin away. It is possible that in the future the bitcoin buyer may not be able to sell their bitcoin for what they paid for it. However, that would be the result of a market consisting of thousands of participants jointly deciding how much a bitcoin is worth.
This of course assumes that the Bitcoin algorithm works as advertised and can not be practically manipulated by a single malicious individual or organisation.