Because of the difficulty adjustment and the economic incentives, the equilibrium cost of PoW approaches the value of the block reward. Even if the result of PoW is useful, then the cost of the "wasted" PoW will still approach the value of the block reward. So, nothing is accomplished by making the PoW generate something useful.
Right. Is using Bitcoin useful? If you agree, then mining a Bitcoin is useful. If it's useful, and uses resources (all useful things do), then you can put a price on it. It just so happens to put a price on itself, and pretty efficiently too.
If you don't understand Bitcoin's usefulness, you're not likely to appreciate how or why the network functions. If you've got criticisms, but don't understand what it's for or why it works the way it does, it's difficult to know how to help the person who feels that way.
Climate change is very real and we need to cut our energy use wherever we can.
Climate change is real, but energy use doesn't affect climate change significantly, there's no evidence for it.
The energy = security thing makes sense until you calculate how much energy one transaction consumes at which point it becomes gross however you want to frame it.
That's thoroughly idiotic.
The energy consumed to mine a block is only used to create new BTC supply, it has nothing to do with the transactions in the block. A miner uses the same amount of energy irrespective of how many transactions they include in the block. A block with 0 transactions uses the same amount of electricity as a block with 3000 transactions.
To put it another way: if energy used = amount of transactions, why is it that the more energy the Bitcoin miners use, that the maximum amount of transactions stays exactly the same? There is no relationship between transactions and energy, that's why