Nobody can predict you the day BTC will end up and so, it also applies to the stocks you purchase online, the metals and commodities you buy. Gold can be $0 any day (take it as an example) because if the demand dies for the same, then it will be worth nothing even if it used to be one of the precious metals some day before. Same is with BTC, its worth completely depends upon how valuable it is in people's lives and the available liquidity to match their demands. So, if you think BTC is a Ponzi scheme, take every single thing that you need in your life to be a Ponzi too. 
Exactly. No one said Bitcoin is a guarantee you'll become rich in the long run. Neither it'll make you profit in a short amount of time. Bitcoin's price is determined by the rules of supply and demand. If there's no demand for Bitcoin, expect it to go to zero in terms of price (which looks very unlikely to happen). The decentralized and open source nature of Bitcoin allows anyone to do as they wish with their funds. Bitcoin is a new kind of money where people are the true owners of the system (not a central authority like it's the case with Fiat today). Those who say it's a Ponzi scheme truly don't know how Bitcoin works. Bitcoin is all about empowering the average person in taking back control of his/her money. Fiat goes against financial freedom since it's largely manipulated and controlled by central banks and governments alike. It's the largest Ponzi in the world, yet people don't seem to care.
Nonetheless, Bitcoin's adoption is growing at a fast pace. People are learning about Bitcoin's true benefits relative to Fiat albeit at a slow and steady manner. It won't be long enough before the average person recognizes Bitcoin to be a truly-legitimate digital currency for mainstream payments. If governments are already recognizing Bitcoin's legitimacy, then why shouldn't the general public do the same? Just my opinion
