Indeed, there are some people that thought bitcoin could replace FIAT. But as have you pointed out it just doesn't make sense or is plausible. Bitcoins are best as an alternative currency. Though there few notes that I'd like to point out from yours. It is expected that bitcoin as of now has volatile prices, but in the future, there is a chance when the market cap grows bigger, the volatility will reduce. And lastly, bitcoin with how it operates right now is a pseudonymous currency, it is not purely anonymous money.