The systems before them, where each local region, each business, each actor, could coin money via IOUs or other forms and trade was much more costly and corrupt than the current system. Local failures, actors running off with capital, low liquidity were rampant.
There are decent empirical reasons the entire world moved off systems tied to how fast they could dig up metal - such systems have an impedance mismatch with productivity, for example, hindering growth when useful and flooding the markets with new gold finds when the markets don't have matching growth. These led to boom and bust cycles.
With the introduction of the US Fed, recessions became less frequent, less damaging, so much so that the period called the Great Moderation still has economists working on exactly how come the previous boom and bust cycle got so smoothed.
After the Great Depression and the resulting solid evidence that non-fiat exacerbated the problem across dozens of countries, every economy in the world move off them. The evidence was that solid.
>Focusing on how cryptocurrencies are "used by criminals" is astonishingly wrong-headed.
Yet it's backed up by factual behavior.
>Two-thirds of the global population are not served by the present system.
Citation? I can find nothing near this claim to be supported by any evidence I can find. From what I can find, a large majority of the world's population has access to and uses bank accounts, and the vast majority of the rest use cash to transact wages and purchases. If pretty much every person on the planet uses some form of govt issues money, how is that not being served? They're pretty much all capable of local barter, yet choose this other system. Maybe it's better for them? At least they're choosing it.
It is true that a decent chunk of the world has no access to a cell phone or internet. How will cryptocurrencies serve such people?
>Once the world's population has uniform access to viable, stable and useful money
Which cryptocurrencies are anywhere near as stable as a modern first world currency? By stable, I mean the usual financial measure of price volatility against a reasonable basket of goods. Last I checked, BTC, for example, was about the least stable investment one could make. Volatility has serious costs throughout the economy - predictability is vastly better for making contracts like employment or rent or mortgage.