Comment by hn_throwaway_99

> In theory, adoption could also increase without much price increase.

Not really. A fundamental purpose for any currency is to act as a "store of value". There is no way for bitcoin to represent a store of value (i.e. value commensurate to real-world goods) for a larger and larger portion of society without the price skyrocketing, especially since Bitcoin is inherently deflationary with a max number of coins.

Regarding your other paragraphs, I think this is a fundamental misunderstanding of how proof-of-work is designed to protect the network. The entire idea behind POW is that the total amount of work must be in direct relationship to the total value of the coins in the network, or else coordinated attacks become possible. I see this misunderstanding all the time in "the block reward decreases over time" argument. It doesn't really matter if miners get their payoff from block rewards or mining fees - they must (on average, over time) get enough reward to make their mining activity worthwhile, and, again, by the inherent design of POW, they need to spend enough on mining to make 51% attacks not worth trying. Just think about how your "If it's using Europe levels of electricity at time X, then after a block reward decrease, it'll use Europe/2 amount of electricity" sentence doesn't make any sense, because eventually in 2140 or so there will be no block rewards, so according to your logic no electricity at all would be required to run the network.

There is simply no getting around the fact that resource costs need to grow linearly with the total value of the network in POW systems.