Not OP, but I think you are misreading their point. They didn't say that having a governing body is a sufficient condition for having a stable currency, they said it's necessary. It might not be a settled question how monetary policy affects inflation, but cryptocurrencies effectively have no monetary policy apart from a ramp decided when they are created. That doesn't take into account lost wallet keys or number of people using it and mining it...
Ethereum is pioneering a new monetary policy with EIP 1559 (which is going live with Berlin fork this summer).
Under EIP 1559, each block will burn ETH — the amount of ETH burned increases as blocks fill up. The ETH burned can offset & exceed the ETH block issuance.
Over time, if ETH block space is full, the amount of ETH will decrease.
Which is, if I understand correctly, a kind of balancing feedback loop. People are spending -> make it deflationary. People are hoarding -> make it inflationary. It will be really interesting to see if this has any stabilizing effect in the (very) long term.
Game theoretically, you want to be the hoarder. Let others spend and you reap the rewards of a deflationary asset. In effect, people will still try to hoard as much as possible, and only spend when absolutely necessary.
That's true as long as there are hoarders and spenders as well. As soon as there are too many hoarders, inflation comes back, and there's personal incentive for everyone to spend.
There is no equilibrium at either everyone being a spender or everyone being a hoarder, thus the self-balancing nature.
