Bitcoins is here to stay after 10 years of existence with all the setbacks from governments, financial institutions , media and even cryptocurrency traders. A system of payment that has existed for 10 years can't be doubted as a ponzi scheme, fraud or scam as stipulated by many naysayers. Hurray!
Indeed, a ponzi scheme would not survive for 10 years like bitcoin. I think bitcoin as a ponzi scheme is just the opinion of some peoples only.
I dont think bitcoin as pyramid or ponz, it is a currency. But bitcoin is mostly used as a currency in underground, that's why there are many peoples who still afraid to use bitcoin as a currency.