But does the security of the network even depend on that? I think it only depends on how much hash rate a malicious entity (such as a government trying to destroy Bitcoin) can control in relation to the total hash rate.

Let's say the US gov wants to destroy it. If the energy prices rise by 10x, the hash rate will drop, which may make the network seem more vulnerable to attacks, but the US gov's hash rate will also drop, keeping their share of the total hash rate (and therefore the network's vulnerability) constant. Unless they can somehow control the use of energy through coercive legislation enforced effectively.

In other words, it depends on the level of centralization of power in the world. Which bitcoiners like to believe Bitcoin will decrease (along the lines of what "The Sovereign Individual" predicts...)