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What your grasping at is that value is still vapor-like. While crypto is different than any other currencies, you can still ask yourself why people accept dollars in exchange for real goods. It's not because the dollar itself has a value, its because of a long confidence that the dollar means something. Is it really different if its a government that represents 300m people that says it has value, or 300 million people not represented by a government that say something has value?
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Taxes. Taxes make dollars valuable. Everyone has to pay taxes, property, income, etc. Therefore dollars are a needed commodity for people and businesses.
Your argument is that government issued currency's value is that the government accepts it back in satisfaction of tax payments. That's so circular that it's scary.
Honestly, if that were the basis for value the dollar would have died a long time ago. People would hold and trade other assets and only convert to dollars when they had to for tax purposes. In fact if that were the sole basis of value of the dollar it would be virtually impossible to calculate the value of the assets you actually receive and trade.
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That is largely what people do. Well people and companies who have a large excess of dollars. They buy stocks, bonds, real estate, and other investments when they have a large excess of dollars. Warren Buffet doesn't have 40 billion dollars sitting in his bank account. He probably has a couple million (at most) in checking and savings accounts. He only converts those investment holdings to dollars when he needs dollars for taxes or for some other large purchase.
And taxes have always been a driver of value of currency, particularly paper currency.
See the British hut tax. This is how they introduced paper currency to their African colonies.
The hut tax was a form of taxation introduced by British in their African possessions on a "per hut" (or other forms of household) basis. It was variously payable in money, labour, grain or stock and benefited the colonial authorities in four interconnected ways, by raising money; supporting the economic value of the local currency; broadening the newly introduced cash-based economy, which aided economic development; and integrating local communities into the new economic system.[1] Households which had primarily been rural ranchers or farmers proceeded to send members to work in the cities or on colonial government-sponsored construction projects to earn money to pay the tax.
https://en.wikipedia.org/wiki/Hut_taxThe paper currency was tradable and valuable because everyone needed it to pay their taxes in. Afterwards it gains an inherent value of its own based on the strength of the economy but the root value of a paper based currency system is taxes. It means there is always a demand for the paper to pay taxes. There are also lots of practical reasons why a currency based economy is much more practical than a barter based economy. But the underlying value of any currency is that citizens of that country need to trade for it in order to pay their taxes.