Well, there is another problem with fiat money. I am not a religious scholar, so, I cannot pinpoint the haram-ness of the practice just like that, or shake it out of my sleeve, but I certainly suspect wrongdoing.
As you know, the United States has a long-standing deal with the oil producing countries in the Middle East that they will sell their oil for dollars and that the buyer of the oil will therefore deposit the money in a New York bank account. This system forces approximately every buyer of oil to get hold of dollars and hence artificially beefs up the demand for dollars. At the same time, it allows these New York banks to control who exactly the oil producers sell oil to. It also allows them to control what they spend their money on. As you can imagine, oil producing countries in the Middle East must pretty much ask permission to their New York bank to sell their oil to any new buyer, and ask permission to spend their money to any new supplier.
As you know, the New York bank can at any time freeze access to the accounts, as they did with Iran's funds.
Furthermore, a great deal of the artificial value of the dollar is that you can buy Middle eastern oil with it. That is what allows the US to print endless amounts of dollars in total impunity. Other countries need oil, and therefore their debased dollars too, no matter how many of them that the US prints.
The rumour goes that the real reason why the US invaded Iraq is that Saddam Hussein was going to cancel this long-standing oil-for-dollars deal. Ultimately, the value of the US dollar rests on the ability of the US to invade oil-producing countries and threaten them into selling their oil for dollars.
I do not know why this would be haram in terms of religion, because it sounds rather like a political problem. Still, it would be a good thing if it were possible to produce a fatwa that denounces the use of paper money, especially dollars. It would even be beter if it could denounce the practice of selling oil for dollars.
I personally avoid using dollars. Everything I do in terms of finance revolves around using bitcoin. Of course, it would be nice if there were some kind of slamcoin cryptocurrency, because I would certainly want to use it too.