It's not about an economic attack on Bitcoin. Miners can be ordered by the government to shut down and will be unable to do anything about it.
A pool is made of many miners, not a farm. A pool IS a farm in the industrial scale mining environment.
They they will just ship the equipment to another country and resume. Not all farms can be shut down at the same time, and if they are located in different countries the harder it becomes.
Also the bitcoin network doesnt need the 3 mining farms, it can even operate with 1 miner. But just the more miners there are the safer it is.
But they wont do that, then the 51% attack is not viable unless you have the support of the bitcoin oligarchs, which they obviously wont get.
So bitcoin is really resilient from this point of view.
But this is getting a bit offtopic here.