Fairly astute observations. Especially on the emotional factor.
However, cryptocurrencies are not a ponzi scheme.
Lets take Bitcoin. It has a set amount of bitcoins. Yes, in order for the price to go up, more people need to trade dollars for it, bidding up the price.
However, it does not collapse if people stop putting in dollars.
Many like using only bitcoin. Exchanging bitcoin directly for services and selling their services only for bitcoin. This is self sustaining, and does not require outside dollars. It is easier to gauge the transaction size, if there is dollar convertibility, but it is not needed.