I totally agree that this is insane - but it is not much more insane than what we do with gold, we dig it from the ground and then put it back to sit in underground vaults. Still I guess gold is much more reliable as a store of value:)
Can you link to anyone at all on Hacker News claiming that cryptocurrencies should be based on proof of planting a tree, or were you making a strawman argument?
https://medium.com/@zby/proof-of-work-8d8265def194
By the way it is important to note that with each block halving in a simplified model (ignoring fees) should reduce the hash power by half.
Proof of Stake might help us here: https://medium.com/@zby/proof-of-stake-can-be-cheaper-than-p... - but it is not entirely clear that there are no holes in the PoS systems design.