A growing pie doesn't refute the opportunity cost argument. Even if you grow the energy supply, you have to consider what else that energy could be invested it,

A growing pie doesn't refute the opportunity cost argument. Even if you grow the energy supply, you have to consider what else that energy could be invested it, be it food, or housing construction, or transportation, or even space travel. Energy is the real currency in this world, convertible between different forms, and mining bitcoin is sort of like an unavoidable thermodynamic loss for doing any work -- a high cost one.