It's just a value store. Debating the efficacy of the value store is fine, labeling it a ponzi scheme seems reductive to absurdity.
The real problem (unsurprisingly) is with fiat currencies. These are heavily regulated, nearly made up values. That crash, often. We put handbrakes on the systems (see gamestop, mortgage debt crisis etc) because of how unsafe they can be.
If we trade goods for fiat currency, we put handbrakes and regulations there too.
The bitcoin/fiat exchange is merely proof why we need these regulations. Until it (the crypto/fiat intersection) is regulated, it's not gonna look and feel like what we're used to.
There are good criticisms to be made of bitcoin (like how centralized most mining operations are, the community's constant in-fighting and many more). It's drowned out by daft arguments like pollution (that's a whole other economic sectors fault) and ponzi schemes.
Maybe other coins could be construed that way (again, regulations required) but not bitcoin.