Following scenario: A government would like to destroy Bitcoin. It buys a significant number of ASICs to build up a huge mining farm and carries out a 51% attack.
From my point of view it will not be so easy to buy so many ASICs as once - what do you think?
Another question: Will it be noticed (how?) that somebody buys a big stack of ASICs and/or are we able to identify such a behavior monitoring the network's hashrate?
You are confused at the difference between a Government Power verses a rich person Power.
You outlined how a rich person would attack bitcoin, by buying what they needed to make a 51% attack.
A government would go about it differently.
1. Just Outlaw it and imprison anyone for 20 years that used Bitcoin.
2. Seize / Confiscate any ASICs warehouse in your or cooperating counties, and use them for an 51% attack.
3. Threaten the top 4 mining pool operators with jail or worse, if they fail to comply with your Government desire for a 51% attack.
4. Tax the miners to make it an unprofitable venture, so the miners close down.
5 Full Scale war, physically destroy all ASIC warehouses with explosives and imprison any bitcoin supporters.
6. Start a worldwide Propaganda campaign how bitcoin is funding terrorism and depleting earth's natural resources,
So bitcoin never gains true adoption, and people refuse to use it , because they consider it disgusting.
This would also correlate with the release of a Government Backed/Controled digital payment system
which would be promoted and accepted as fiat in that country.
* While governments may never go that far, be aware, they have access to resources that mean they never have to buy 1 asic to destroy bitcoin. *