Up-thread, the proposal is to fix the scalability & energy usage issues by having a trusted authority such as the U.S. government run a database with a payment API on top.
Under such a system - how do you know that there is anything behind the government's numbers? They could be pure fiction right now and no one but the government would know. Also, the government takes a cut. As the whole economy flows through their currency, they become a de jure taxing body. Their taxes drain the economy, and can be used to manipulate the economy to the government's whim.
It may shock you to learn that not everybody trusts the U.S. government. The growth of cryptocurrencies worldwide is largely fueled by the fact that the set of people who don't trust the U.S. government is larger than the set of people who do - and in fact, they've seen their biggest up-take in societies like Zimbabwe and Venezuela where trust in civil monetary authority has completely collapsed.
You are correct that it wouldn't bring any sort of additional guarantee of the money being backed beyond what fiat currency already has. But, the advantage is that it could be proven, mathematically, that each bit of the currency was actually issued by the federal reserve and is actually backed by the government. As it is now, it could just be a bug, or malware, or pure fiction invented by a company to make their numbers look better. And you can't prove that either way.
I am no economist, but I have never thought the idea of "trust" had much to do with the value of US currency. Certainly it's not backed by gold any longer. But I think it's backed by something real. Bombs. The US has more than enough to force others to accept their currency as having value.
Under such a system - how do you know that there is anything behind the government's numbers? They could be pure fiction right now and no one but the government would know. Also, the government takes a cut. As the whole economy flows through their currency, they become a de jure taxing body. Their taxes drain the economy, and can be used to manipulate the economy to the government's whim.
It may shock you to learn that not everybody trusts the U.S. government. The growth of cryptocurrencies worldwide is largely fueled by the fact that the set of people who don't trust the U.S. government is larger than the set of people who do - and in fact, they've seen their biggest up-take in societies like Zimbabwe and Venezuela where trust in civil monetary authority has completely collapsed.