Any viable large-scale retirement system is going to be a Ponzi scheme, because the "old investors" (retirees) are going to be dead soon and the only way to support them is to recruit "new investors" (working-age people). Tontines, life insurance, bank deposits, the stock market, 401(k)s, pensions, cryptocurrency, whatever - when you unravel them deep enough, they're a Ponzi scheme. This applies to even safe, conventional investments like a bank savings deposit: what's really happening there is that you amass a large credit over your lifetime, and then when you need extra care and support and can't work for it anymore, you transfer that credit over to a working-age nurse/etc so that they can build the same sort of credit for their old age. People who don't budget for this properly grow old destitute and unable to convince anyone to aid them.
In this regard, it mimics life itself. At some point the body gives up on repairing all the cellular damage that's accumulated and just hopes that it's made new humans along the way.
Civilization is built on all the side-effects of humans chasing Ponzi schemes. The reason governments ban actual Ponzi schemes (in the sense of "Everybody send me a dollar and pass this on, and I'll give you a $0.50 for everyone you recruit") is because it incentivizes the citizenry to do nothing other than create and participate in Ponzi schemes. Meanwhile activities like founding startups or trading stocks - which are every bit as Ponzi as that - are legal because the pursuit of them creates beneficial social effects (like innovation, price discovery, and capital allocation).