The funny thing about bitcoin being called a ponzi, to me, is that there used to be (not sure if there still are) many many different ways to get free bitcoin. lol. There were faucets and ad campaigns and such that you could take advantage of and get "free" (Doing a task isn't technically free... lol) bitcoin in the process.
What ponzi have you ever heard of, that gave you free entry? And then allow you to keep getting money free? With no investment? :P
I haven't heard of any, at least.
Also, bitcoin made no promises to anyone! Bitcoin itself never said "I'll make you tons of money! Just buy X amount of me!" Our beloved Bitcoin has never asked anything of any of us. Except for us to love it. lol
People relish intellectual comfort. Thinking is the most energy-expensive task we can do, so many people have devised mechanisms to allow them to save (scrimp) on thinking. Labeling something as, for instance a "Ponzi scheme" without looking closer allows one to "safely" avoid thinking ...