only with a number associated with their bitcoin address. Since this number cannot be practically utilized like food or dollar, that means that investors engaged in a one-way transaction.
The dollar or any other fiat currency can not be practically utilized but are assigned a value by the banking sector of their country of origin. The dollar has no intrinsic value, no equal effort is put into making it, $5 cost as much as $100 bills.
Bitcoin is also a currency which is assigned a value, not by the banking sector but by the community as it is decentralized. And this value is designed to be higher than the cost of production.
The problem lies in the fact that you see BTC/USD pairs on exchanges, and it appears to be pegged to the US dollar.
With increased adoption it would gain more practical use and can be easily pegged to commodities or labour.
Of course there are limitations to such level of mass adoption, but that doesn't make it a ponzi scheme or a one way transaction protocol.
Completely agreed to your point, even if we think about gold, its just a metal but high demand has increased its value else its not a necessity for anyone, being a decentralize currency Bitcoin is accessible to everyone and w/o any third party intervention, its the common people who increase or decrease demand, one need not to be worried about bitcoin physical presence or its use till the time it has high demand.