Bitcoin is a pyramid scheme. I get it, some people understand it and they are OK with scamming from BTC. But those who do not understand it... are in real danger of losing tehir hard-earned money.
According to Wikipedia:
A pyramid scheme is a business model that recruits members via a promise of payments or services for enrolling others into the scheme, rather than supplying investments or sale of products.
I was never promised payments for recruiting other Bitcoin investors. Were you?
You could argue the Bitcoin market operates by
the greater fool theory -- people invest because of an irrational expectation that prices will always rise, not because of intrinsic or fundamental value.
That's about it, though. Anyone claiming that Bitcoin is a Ponzi or pyramid scheme doesn't understand how those work.