Deep. Very deep. The exact same thing can be said about money. It only works only if people agree it works. When you exchange your work for money, you are taking a risk. When you keep your money in the bank you are taking a risk. What if all of a sudden everyone stops accepting money?
I really wish we would stop with the Ponzi scheme non-sense. Nobody believes that there is some sort of economic activity that is sustaining the growth. It’s really no different that buying stocks on an exchange. Risky? yes. Speculative? yes. Ponzi? Nope.
This Bitcoin - Ponzi scheme association is used to fear-monger and to stop people from ever learning about it (you don’t want to be the sucker that falls for the scheme, do you?)