Wrong question. It implies energy can only be used exclusively for single purpose. The right question is given X watts, what is the ideal distribution for Y purposes and the answer is that we dont know but we tend to value some things more than others and that will be reflected in the distribution
> no benefit aside from securing the ledger
This is the crucial point that many who raise the same objection dont get: proof of work has to be futile by design. In fact it is misnomer and the correct name should be Proof of energy spent, as the energy is the ultimate resource we’re paying for security of the ledger. If we accept that ledger security must be tied to solving some more “important” problem, and there indeed was a non futile problem space, some f(candidate) that yields two results: (candidate-ok?, problem-solved?), the incentive to search that space drops to zero because it is no longer tied to solving the “important” problem. And suddenly the ledger is useless.
If you know how to resolve this conflict - publish a paper and you will be the next Satoshi.