IMO it's not Ponzi at all , bitcoin is a currency that can be use for investment especially like ponzi scheme, they offer unreasonable profit by investing bitcoin.
Some people afraid but if they are dare to take the risk, you will see that bitcoin will make you rich
The question is how long they will be rich. It seems to me that bitcoin price is really overpriced. It means that someday she will fall sharply. Who can with 100% accuracy to predict the behavior of bitcoin? I think that everyone should make for themselves an informed decision. Investing in bitcoin is very high risk but the prize can be very large too.