Now, let's assume that indeed Bitcoin is threatening the US dollar, and the US who spends 13 billion on a Ford-class carrier won't be able to pull that off?
I'm just saying that there's no reason to do it. Spend more than a billion dollars to attack something that works under a general agreement. You may indeed achieve to destroy the Bitcoin network, but you won't get rid of your worries. Proof of stake cryptocurrencies will then arise. What will they then do? Buy half of the units? There will be other permissionless and borderless cryptocurrencies they'll be afraid of; beating Bitcoin doesn't beat this liberated attitude.
Once the value is gone so is the hype. The idea for which Bitcoin was created get's more tainted every day, look at the ecosystem now, it's all about centralized exchanges and wallets, prices and trading, and holding till you make x in profit
Yes, this is how the world works, I know. The majority of the people don't want to be responsible for their wealth. Hence, centralization occurs.