Thank you for your response. This will become an interesting discussion since, when I first started studying these things, my thoughts were mostly the same as yours. Only when I started to reflect on the standard economic curriculum and narratives that I realized that economics, finance and money are very political in nature.
Fiat is very misunderstood. The best way to explain it is to look at the alternative, the gold standard. Given that gold is in limited supply (2% growth per year, much lower than economic growth) any gold standard will mean deflation when you have economic growth, so the value of gold reflects the new value being created.
It's even fairer to say that the gold standard is very misunderstood!
The idea that the gold standard is harmfully deflationary is based on the history of central banks trying to hang on to the gold standard *after* a financial bust -- that is, too much paper wealth had been issued and confidence in the paper was lost. At the right ratio of gold vs. paper assets, say in the 1860s and 70s, the gold standard was a factor favoring prosperity and stability across the world.
And why was too much paper issued? It goes back to to the incentives for the financial and political elites to benefit from issuing assets and propping them up with public power. In this regard, the gold standard is not fundamentally different from fiat money, though its speed of blowing bubbles may be slower.
The humane response, after a financial bust, would be to devalue paper money against gold. But the top global elites have been very reluctant to do this over the centuries, for the purpose of protecting their long-term prestige and power. (Thus, the Federal Reserve did nothing in the early 1930s as the Great Depression turned truly ugly -- only in 1934 was the dollar devalued, by only about 50%.)
And deflation is very bad long term. It stifles trade because why buy something today when your money will be worth more tomorrow? Deflation creates a game in which the person who can afford to move last wins, as in very in favor of the ultra wealthy. Which means that with deflation they cannot go bust anymore, all they have to do is keep their money safe and deflation will do the rest, but with inflation they have to move their money otherwise inflation will erode their wealth in time. If you look at US history you'd see deflation causing depression in times where capital was flowing into the economy. Inflation stimulates the economy, the person who moves first has the most to gain because money is losing its value constantly.
This is certainly one of the standard modern economic arguments. But it's incorrect. Everyone is eventually incentivized to spend, as their savings get bigger and their days on this earth get fewer. Money does no good to oneself unless it's spent.
Inflation can be good or bad, and deflation can be good or bad (good as in encouraging future planning, ie thrift and investment as opposed to consumption.) Inflation and deflation will always be with us. The key issue is not inflation vs. deflation, but what forces drive each one. Is it driven by market forces, or by elite central planning which history has shown is always in favor of the elites and at the expense of everyone else? And fiat money is a major pillar of power for the elites.
Fiat is a very elegant solution to the problem of deflation. When you had a gold standard money was synonymous with value. But Fiat is not just value, fiat also stores debt because a debt is being made every time money is being created and our financial systems are set up in such a way that value rises to the top and debt sinks to the bottom. Bank bail outs meant the people at the top kept the value while the people at the bottom were stuck with all the debt. That is the problem, not fiat per se. But as long as fiat will be controlled by bankers and governments you'll get crap like this.
Since fiat money is controlled by elite members of governments and central banks (which is the definiation of fiat money,) it will only ever push value up and push debt down, as it has done historically. (In fact the gold standard is basically the same way, though in a less extreme and slower fashion -- after all, it was central banks who designed gold and silver standards. This is why the gold standard is very misunderstood by everyone!)
A truly just and enlightened system is one where public power has no role to play in the value of money or any other asset. As soon as government issues money, the prestige and economy of the country is being used to support its value. Distortion, and every other bad thing, happens from that point on.