This point hinges on the assumption that bitcoin itself doesn't provide any benefit to humanity. If its a useless speculative asset with no purpose other than

This point hinges on the assumption that bitcoin itself doesn't provide any benefit to humanity. If its a useless speculative asset with no purpose other than as a ponzi scheme then yes, all energy used towards it is a huge waste and needs to be eradicated immediately. If it has the potential to allow people to save their wealth under unstable regimes, as a long term hedge against inflation, as away of getting people to save more instead of spending every penny they have before it depreciates, to cause real wages to rise again, to encourage actual economic productivity rather than continually investing fake printed currency into an endless series of economic bubbles producing significantly more environmental damage than anything that could occur as a result of bitcoin mining.... then it is not waste.