You're really reducing a whole economic situation to a currency issue ?

It's a confluence of various factors. Explosive population growth, for example. The modern economy (of which fiat currency plays a pivotal role) relies on that of course, as the lending system is a bet on future growth. If that fails the whole thing can enter a state of catastrophic failure. But population growth has more precedence. Fiat currency, bureaucratization, etc. were adopted as reactions to increasingly explosive populations and unchecked rationalism developing the absolutely ridiculous modern state system.

If you want demons to point a finger at, you're going to have to look further back in time than the 20th century. Then and now we're just doing a frantic tap dance to keep what we inherited from catching on fire.

No, fiat currency has allowed our money supply to track closer to our GDP, preventing currency shortages and price manipulation by foreign adversaries, giving us the most stable economy the world has ever experienced over the last 50 years. Yes, it can be abused (and some Asian countries have taken this to dangerous extremes), but it’s better than all the alternatives so far.

The good standard didn't even last half a century before collapsing.

Gold is way too inelastic to work as a basis for currency in an industrial economy.