You can also not use euro to pay for your federal taxes in USA. You can however convert your euros to USD in order to pay for them. If you think euros are more trustworthy and give you full self custody, then it's a good reason to hold your money in euros . Plenty of people do that in the world; they store their money in USD rather than their inflated less reliable national currency.
Victim to speculation? Unfortunately yes, but same thing goes for stocks, even basic foods and raw materials nowadays. What do they give you? Whatever matters to you: full privacy? Full ownership? Freedom of movement for your money? Not one central entity deciding on the amount that's printed? Voting power in the tech that's being built? Most stocks nowadays don't give you anything as well, but the fake belief on how much it's worth and a lot of people agree nowadays they don't represent true value of the company in many cases (Apple, Facebook, Tesla, etc.). You don't get voting rights, you don't get dividends. A lot of Cryptos do give those.
Having said those counter-arguments, of course there's flaws too and frankly more with the majority of them. It's those select few that could matter on long-term