Opinion 1:
BTC is a Ponzi schema, the reason why I accept it is because I believe there will be bigger fools to purchase it from me.
Answer:
In that point of view, US Dollar could be viewed as a much larger Ponzi schema. The reason why you accept US Dollar is because you believe someone else(or maybe everyone else) would accept it.
I don't believe that Bitcoin is a ponzi at all, but I don't think it's at all comparable to USD in this context. Bitcoin is said to be a ponzi because
speculation drives its value
up -- this is where the belief that some other person will buy it for a higher price comes in. That trait
very loosely fits with the narrative that a ponzi is a scheme where older members benefit from the new members coming in. It's very different from a person accepting USD because it's legal tender, where there are no speculations involved.
a Ponzi scheme actually requires more centralization where someone takes your money as an investment and then pays the older investors from that money.
bitcoin price is set on a free market, if we starts calling this market a Ponzi scheme then everything else in the world is also a Ponzi scheme! every object is prices this way, it is not just USD