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?