Fiat currency is an excellent mechanism for stealing wealth from a population without them realising (well realising who took it at least). Each time they create credit (i.e. print money out of thin air), they don't create value, they simply dilute the value of the money supply across more monetary units. The value in the newly printed "credit" comes from the existing money. That's why prices go up endlessly. It's not the value of things we buy increasing, but the value in our money leaking away into the money they are creating. The reality is that value of most consumables (food, electronics, cars, toothbrushes etc) is going down year on year by ~5% but by increasing the money supply by ~7% each year, we actually see prices increase by ~2% average (CPI).

It also distorts other fundamental signals like GDP. Devaluing the unit of account by printing money makes the GDP figures go up because you're measuring it with something that's going down in value. Looking at the USA and accounting for money supply increase, it has had falling GDP for decades.

Money is proof of work, or it should be. To create it should take as much work as it's worth (this is true for both gold and bitcoin). In reality, fiat is proof of work for the population, while the bankers have a free money spigot. They can pour trillions of it out of nowhere with a few keystrokes and then charge interest on it for decades to come, as if it was their own money.. It gives them undeserved, unlimited power.