[Cryptocurrency] isn't a "Ponzi scheme". Even if you believe that investing in [Cryptocurrency] makes no sense, and it's a useless [tech] with no practical purposes, and it's a bubble waiting to burst and so on, that still doesn't make it a Ponzi scheme.

Even if all of those beliefs above were true, it still wouldn't be a Ponzi scheme. As someone else posted in here, Ponzi Scheme has a fairly specific definition which "[Cryptocurrency]" doesn't meet.