Government state can print unlimited amount of money. Beside, what if they don't even have to purchase the ASICs? They can just confiscated the mining equipment from miners (very plausible in authoritarian states like Russia or China where government has lots of power).
Unlike what people think, governments cannot print money at will. There are severe repercussions when a government prints money at above normal rates, which actually could result in a failure of the economic systems.Governments, at least as of now still rakes a significant portion of money through cryptomining by the employment, taxes, ASICs manufacturers, etc. There is just simply no incentives for them to kill of the whole industry; an attack like this happens once. After that, the attack gets exponentially harder to reap any benefits and another Bitcoin with a different algorithm springs out. You have just wasted all your ASICs and your electricity and crypto survives.
In PoS it's actually exponentially more expensive to sustain an attack as the stake of the attacker is destroyed. They would have to keep buying coin from a decreasing supply at an increasing price, which would tend to infinity.
In PoS, you are not exchanging anything. PoW functions on the premise that some form of resources is being used up in exchange for getting a block. If those who holds a greater "stake" are permanently at an advantage, then why wouldn't the network be worse off? What would be the deterrent if the government manages enough resources to seize/purchase enough funds? 
