My point is it also goes in the other direction (not to understate how ridiculous bitcon's energy usage is, though): the reward in BTC reduces exponentially over time (this is why there is a finite amount of bitcoin that will ever exist). Even if the value goes all the way to the moon, the rewards will eventually peter out (though it might be on the scale of many decades: the reward halves every 4 years or so). This means the cost of sustaining the 'value' stored in bitcoin will need to fall on those who own that value (lest it be stolen), and that could be very expensive compared to other forms of value storage.
Bitcoin could very well be simultanously ridiculously inefficient and yet have insufficient incentive to keep mining at a secure level long-term.
Right. Including the invisible fees (due to increased BTC supply accruing to the miners), a transaction right now costs around USD 100. As the mining reward drops, either miners make less (good, they'd stop wasting), or fees paid by the user would have to increase substantially. If users don't pay up, there'd be much less hash power devoted to the system, rendering it insecure.
Agreed - it stands to reason that as BTCUSD rises, more miners will come in until the electricity and electronics wasted per day reaches a certain, relatively fixed proportion of the daily block rewards (900 BTC/d until 2024, currently about USD 35m per day). With that, BTC now consumes about 0.5% of world electricity. If BTC goes 10x, its electricity consumption could approach 5% of world electricity consumption - insanity.