Store of value is a legitimate use case. How bitcoin is useful for that is debatable, but cryptocurrencies do have some advantages over precious metals. There should be a niche for 'internet gold' (https://medium.com/@zby/proof-of-work-8d8265def194).

The energy wastefulness is proportional to the block rewards and fees, the rewards will be exponentially declining to zero and fees should be proportional to the usefulness of the system. Also most probably some other more efficient cryptocurrency - possiblly PoS or DPoS based (https://medium.com/@zby/proof-of-stake-can-be-cheaper-than-p...) - will replace bitcoin.

Having said that - yeah - there is just too much scam in all of this crypto-world, this will end up badly.