> If there was a stock that advertised it self as never going to pay dividends/buybacks, I'd totally call it a ponzi scheme.

I kind of understand what you mean, but I still feel like that situation would be different than cryptocurrencies. If you are buying stocks you have an ownership stake in the underlying asset. For example, you have the ability to affect change in the policy not to pay dividends/buybacks. So in a sense even in this case you still have something of value.

But with cryptocurrencies you can't affect others in this way. You are all entirely independent actors and the value of your currency is really what someone will pay. It's just a medium of exchange no more no less.