Just to put that "colossal waste of resources" in perspective... allegedly we're wasting 60 TWh/year 'mining' Bitcoin, and this is considered (maybe rightly) an environmental catastrophe.
We also use around (again allegedly) 220 TWh/year mining Gold.
I don't want to start a "Bitcoin is useless" flameware but to your question: the reason why the energy consumption of proof-of-work is important is because society hasn't found a purpose for Bitcoin to exist yet. Therefore, the energy consumed is considered "wasted" whereas it could have been used for something society already deems useful, like keeping the lights on.
