I think bitcoin is number 1 to be used as an investment for old age, bitcoin will be adopted by many countries in the next 10 years. Fiat will disappear and bitcoin will dominate it. For beginners, don't be afraid to invest in bitcoin because bitcoin is the best choice compared to other assets.
The intention was to create an alternative currency that works viz vice with fiat, bitcoin is never against the use of fiat but its a freedom currency which I prefer to call a paradigm, it's all about having full control over your finances which is the direct opposite to government desire, the governments does not appreciate anything that has do so much with privacy, freedom and that's why bitcoin is usually getting attacked by governments even though we see less of such case this days.
most of the idea that tend to suggest that Bitcoin was created as a replacement to the fiat only shows that the individual has a wrong knowledge about Bitcoin and doesn't even understand the whole essence of Bitcoin creation. The best way to look at Bitcoin which an average person that's not still conversant with it purpose will easily understand is that
Bitcoin is an international decentralized digital currency while fiat is a per nation centralized currency. the creation of the latter doesn't mean that the former has lost it value. It only suggest that with Bitcoin, you've been given full control over your money and that you've gotten the ability to make transaction accross different national boundaries at whatever time you want to with zero restriction of any sort.
smart investors will only make Bitcoin their main investment, and when they need money, they will use the Bitcoin they have as collateral in a lending platform, they are very smart because they realize that there are only 21 million Bitcoins and the amount cannot be increased or decreased.
No, no, no! Anyone using his bitcoin investment as a collateral is no worth regarding as smart because it makes no sense using your bitcoin to take loan on fiat. This is why we are advised to while planning on investing for a long time we also have a reliable income source if possible a stream's of income in order to avoid finding yourself in a messy situation where you would have to make such unwise decision because it's like telling an investor to stake his bitcoin for an altcoin.
the fact that he sees this idea he suggested as being smart is what even baffles me. Who makes an investment because he wants to use his investment as collateral for obtaining loan? If buying Bitcoin is all about such purpose, then most persons wouldn't consider investing in Bitcoin because it will totally look worthless. I don't even know why he's trying to relate the 21 Bitcoin in circulation to the reason one will go on to gamble with his investment by using it as a collateral for loans.
Owning Bitcoin is a precious previledge I wouldn't give away for any reason. It's reckless, careless and unwise to think that your accumulated Bitcoin has gotten less valuable to the extent of trading it in exchange for fiat which is far less reliable compared to Bitcoin.