It's the same situation as gold and gold mining. The marginal cost of gold mining tends to stay near the price of gold. Gold mining is a waste, but that waste is far less than the utility of having gold available as a medium of exchange.
I think the case will be the same for Bitcoin. The utility of the exchanges made possible by Bitcoin will far exceed the cost of electricity used. Therefore, not having Bitcoin would be the net waste.
Well we have this post from the satoshi he made in the forum about Bitcoin mining being in the same sense as mining gold which you are correct but I haven't seen any kind of statements regarding Bitcoin being the same as gold in monetary sense. Since if you look at his statement you will see that satoshi himself doesn't see any much utility for gold in a form of medium of exchange which unlike Bitcoin being a digital currency and all has far more acceptance in various businesses, so I really doubt that Satoshi made a comparison way back then comparing Bitcoin to gold in a monetary kind of way.