And replacing unstable fiat money with even less stable, totally speculatory crypto like Bitcoin? Seems like it's better just to buy some USD and stash it somewhere. Hell, even buying and reselling Steam keys is probably less volatile.
On the other hand, without the PoW mechanism of Bitcoin, it's impossible to have the properties that bitcoin has - global decentralised money and payment network. If you believe otherwise, make one! Very quickly no one will be willing to pay for Bitcoin, and all those "wasted electricity" will suddenly become available again.
To be clear, I'm not saying either of these is "correct". My entire point here is that everyone talking about "waste" is just imposing their own private value system on everyone else and I've yet to see a single person apply some kind of consistent standard for what should and shouldn't be banned
The difference is that, for videogames or mining physical rocks, the power use is an undesired side effect, so the incentive is to minimize it, while for POW cryptocurrencies, the power use is an essential component of the mechanism they use to prevent double spending, and the incentive is to use as much as possible.
POW could be replaced by the more efficient POS, but network effects make that highly unlikely without government intervention.
Just because you do not derive utility from something does not mean it a waste and should be banned.
I'm not sure which of the many consensus protocols you may have in mind, but proof of stake is the most popular alternative.
A 51% attack for PoW requires that someone can afford to power 51% of the network. That's expensive. Once the attack is detected, the community can fork away from the moment of the attack.
A 51% attack for PoS requires that someone owns 51% of the tokens. At that point, the attack costs nothing. If the attack is detected and the community forks, the attacker still has enough tokens to attack again on the new network - at no cost.
All of this stuff is brand new. Saying that any of it is "proven" is pretty bold.