Would it mean there would be less interest in mining bitcoin (and thus 'wasting' electricity)?
The reason why is that electricity for mining is priced in national currency, so interest in mining bitcoins depends on a miners future expectation of the value of bitcoin price in national currency when they sell the bitcoins to pay the electricity bill. The current wisdom is that the halvening decreases the amount of bitcoin that miners receive while increasing the USD value of bitcoin because it decreases market supply and the perception of market supply.
If the price of Bitcoin now doubles presumably no miners will be turning off their machines. If it doesn't double, some fraction of all mining setups just became unprofitable.
Fees are still not near dominating the rewards so we do expect to see miner revenue drop due to this.
First thing, even if the block reward is zero, there are still transactions fees. We are not here yet but they are expected to be the primary motivation in the future.
Second, difficulty scale proportionally to the global mining power so that one block is mined every 10 minutes or so. As rewards decrease, the most expensive mining operations will shut down, keeping the cheaper ones profitable. An equilibrium will be found.
The last point is a problem as it makes the network more centralized, potentially allowing for 51% attacks.
We know that the expected return from newly minted bitcoins will reach zero at some point in the future.
We don't know if expected return from tx/fees will ever hit zero.
TBH if it ever got back to the point where I could mine a block every couple weeks with a GPU, and I had access to a GPU, power source and internet connect I'd probably start mining again.
IMO Bitcoin exists as an interesting and historical concept in too many people's minds for mining to ever stop. The real worry would be that mining drops off to the point where 51% attacks are viable on the bitcoin mainnet.
We'd potentially see that if many large miners either started renting out their services to the highest bidder or sold all their miners. Once we see more hashpower for rent or purchase than goes into honest mining we have the potential for a 51% attack.
I doubt that. Look at the recent oil production issues: despite demand falling off a cliff, and the price of oil following it, production (supply) hasn't dropped anywhere near enough to match the fall in demand. It's basically a game of chicken--keep going at full force, eating your losses, in the hopes that your competitors are weaker and will be forced to fold before you will.
It's better to consider it as miners subscribe to a lottery (for the cost of their electricity). Roughly every 10 minutes someone wins that "block". Yesterday the reward for winning was 12.5 BTC per block, and now it's 6.25... the cost of entering hasn't changed.
There's more to it of course, e.g. as the difficulty adjusts as in line with the hashrate on the network, but lagged by roughly a couple of weeks worth of blocks being mined. Fees in any given block vary, which are added to the block reward. Many miners pool rosources and each share a fraction of the reward. Etc.
EDIT: sorry for the silly remark, ironically, the original comment stands at +10 at the moment after starting deep in the negative.
Perhaps things like Cardano (https://www.cardano.org) or Polkadot (https://polkadot.network) are better?
Clearly, the benefits for any energy consumption should be seen from the point of view of the consumer. They wouldn't do it if it were of no benefit.
It would be more fair for you to describe the distributed ledger clearing as of no value to you. Because it definitely has a value to some folks.
That said: some other cryptocoins do indeed provide a ledger like bitcoin, still decentralized and trustless, but without mining (and without block rewards).