You shouldn't blame those who say Bitcoin is a Ponzi scheme, we only need to educate them more. Should we talk about the frauds that are going on in the name of Bitcoin and are well linked to a Ponzi scheme? Or should we talk about the way Bitcoin itself is structured that people mistake for a Ponzi? It takes more explanation to convince some people that Bitcoin is not a Ponzi scheme but a blockchain/investment/trading/payment network that is taking the world by surprise.
Or we should ignore such people if they are too stubborn: after all, BTC is not for everyone, those who want to know more - they will try to make things up themselves properly.
I don't buy your idea, there is sense in no sense at times, so blame no one entirely.
We may try to find points for Bitcoin not being a Ponzi scheme for many reasons, but just like stocks and others, including Bitcoin, is it not the people's investent that they designed for A to pay B? Bitcoin is not different if they argue it out. The only difference is that the government assented to its modality in the financial market.
I put it to you today in stocks/shares, if all shareholders are to be given back their money, will they all receive their money? Certainly not! This is the same with Bitcoin if the truth be told. It is the HODLers who persistently sustain the system.