I am not an expert in this area and have never used virtual currency. That said, I vaguely recall governments already making it hard for some currencies to be converted to regular fiat currency. I don't know the implementation details, but I assume that if you can block conversion or transfer, then the money can only be used within the virtual currencies own network. If enough governments or central banks from enough countries align with this, they can make the currency harder to use internationally or at least limit its functionality. I don't have any references for this, just passing vague memories of news reports being submitted here.
The point TFA is making is that the US government can force holders of bitcoin to sell their bitcoins to the government. And, importantly, they can do it via the Fed (which is nominally a private institution), thereby avoiding any politically messy legislation.
The Fed can do this by launching their own bitcoin exchange and then dominating the mining of blocks on the blockchain (AKA a 51% attack). They can then prevent any other miners from being able to mine blocks, and they can configure their own miners to only accept transactions which are depositing bitcoin into the own exchange's wallet.
At this point nobody can sell bitcoin to anyone other than the Fed's exchange, at any price, because the transaction will not be recorded in the blockchain. The Fed can now set the exchange rate to whatever they want, and they can pay for the bitcoin they exchange with whatever instrument they want. They can run the money printer to buy your bitcoin with USD, they can make you accept US treasuries at a certain price, whatever makes the most sense for their balance sheet. Your alternative is to HODL and never be able to sell your coins.
The network would be forked long before all of that could be setup. Millions of developers around the world working towards a goal generally move faster than governments.
The Fed is (nominally at least) a private institution. They are not hobbled by government bureaucracy. Just look at all the things they did in 2020 that everyone would have imagined would have been impossible. All they need is the green light to do it, and the Fed can swoop in ninja style and get stuff done, as they do. There is no oversight, there are no constraints.
I have seen no evidence that central banks are as agile as you claim. Changing a number on a central database is not impressive and doesn't prove they can execute a much more technical attack on a well defended network.
Central banks are more fragile than the Bitcoin network and they definitely don't have the support of the masses. I expect they would lose a lot more than just money in this attack.
Bitcoiners would love to pull these institutions out of the shadows and I don't think central banks survive when exposed to sunlight. Just a small community of coders caught wind of how CBs operate and constructed powerful platforms to carry out large scale speculative attacks on them. Imagine what happens when a few billion people understand how CBs operate... their days are numbered.
Running a 51% attack is not rocket science. It doesn't involve inventing anything new. When they can print the money to fund it it doesn't even require a business plan. All they need to do is buy up enough hash power and they win. Come on now, if there's anything we can learn from 2020, it's that the Fed is extremely efficient at printing money to buy things to shore up their fiat monetary regime.
Did you RTFA? It's like 20 lines of text, that's exactly what it explains. Any entity with the ability to print money can simply buy a dominating share of the hash power and force all the honest miners to either sell out to them or go out of business.
the network is only global and decentralized to the extent that the miners operate with a profit motive. The government that prints the world's reserve currency can afford to print more money than honest miners can afford to lose. Game over.