How are you coming to this conclusion? In addition to the coinbase, miners earn fees, which are valued according to current market conditions (supply and demand)
https://www.reddit.com/r/BitcoinMarkets/comments/7hvj8e/dail...
If Bitcoin becomes the most valuable asset class in the world by two orders of magnitude (in 2020, assuming same rate), lots of crazy other side effect will occur.
Bitcoin isn't going to keep growing this fast. It'll go parabolic for a while, and then settle at a midpoint between where the rally began and where it peaked.
Bitcoin isn't to blame for cheap energy. If it is too cheap, take it up with the people selling it at that price.
Bitcoin does include a perfectly good mechanism to balance security vs cost: the transaction fee market. Users decide how much they want to pay in transaction fees.
The reason for the high electricity use today is the temporary block reward for mining each block. The block reward halves every three years. Once it goes away, the only thing funding Bitcoin's electricity consumption will be the transaction fees users pay. Obviously if Bitcoin does not provide enough value to users, they will not pay high fees. Electricity consumption will naturally go down to a level that matches the value people get out of the network.
Remember this next time you see an article complaining about Bitcoin's electricity use. I haven't seen a single article about this written by somebody who understands the difference between the block reward and the transaction fee market.
The beauty of the mining mechanism is that having transactions processed provides security at the same time. As long as users see value in having transactions processed they will be willing to fund miners with transaction fees.
However, you're right that users aren't paying for security directly. The fee market may not actually give miners enough revenue to ensure network security. When the block reward goes away electricity consumption will certainly drop (relative to transaction volume), but it may even drop too far to the point where the network is no longer secure from 51% attacks.
Even if fees were zero and block rewards didn't exist, people who had bitcoin would mine so that no one else could mine and trivially double-spend (and thus devalue their bitcoin).
The value of mining is based in no small part on how valuable bitcoin are since mining is what preserves that value by preventing attackers from destroying it.
What's worse, the needed amount of electricity to secure an amount of bitcoins is relative to how much energy an attacker can expend, not some constant value which will remain low.
Completely undeserved IMHO. Vastly more energy is wasted by sillier things. For example worldwide Christmas decorative lights consume 2.3 GW annually (assuming it's 3× the US), which is a lot more than Bitcoin (I estimate ~1.7 GW: https://news.ycombinator.com/item?id=15858966) and yet I don't see nearly as many news article criticizing Christmas lights for using so much electricity... Hence why the criticism is undeserved/unfair. If we can afford to power silly feel-good lights, surely we can afford to power a revolutionary decentralized permissionless censorship-resistant financial network.
Don't forget that one of the sources cited—Digiconomist—overestimates consumption by ~2×: http://blog.zorinaq.com/serious-faults-in-beci/
But even though the articles I've seen are pretty fluffy, they probably stem from an underlying issue that makes Bitcoin different from traditional, energy-heavy industry: The value produced is not directly connected to the energy expended in production. Bitcoin would work just as well with a small fraction of the hashpower it has today. Security is an issue, but surely it must be over-secured many times over at the moment.
Unfortunately no mechanism seems to exist to balance security vs cost, except for the crash-boom market cycle Bitcoin constantly goes through. How much hashpower is needed? The question is moot as there is no way to moderate it, and I'm starting to think that may be Bitcoin's biggest design flaw. (Market forces will certainly bring the energy cost of mining down one way or the other, but it's not clear how much damage will be done to Bitcoin in the process.)