Hmm, interesting. However, is it proper to compare what nature does to human with what human does to human? Ponzi is a form of fraud made by humans effecting solely humans.
There are legalized ponzi schemes, such as the social insurance/pension system.
I think it's advisable to say that laws exist to protect the society. Legalization happens from the state to supposedly protect/take care of you. Yeah, pension looks like a pyramid, and many other things in life too. That's why the ponzi, as a term, is strict.
Besides, ponzi is by far a big fraud. What fraudulent does the pension system have?
I would call it a scam, but it's legalized by the state. Just like there's legalized violence (police) and legalized money monopoly (fiat currencies issued by private central banks like FED/ECB).
I agree about the latter, but for the former, I'm not yet convinced.
So it doesn't matter if it's a scam, what matters is if it's legal
Do ethics matter?