If people won't buy your fish for the cost it took you to get it to them then you'll stop fishing because that signals increased supply and/or reduced demand. (N.B. I'm talking all costs here - assets, labour, opportunity, knowledge attainment.) If BTC mining becomes a bigger operation then you can bet that the bulk of those costs will be fuel for the rig and that will be damn close to the BTC price as it is with everything else.
An oz of Gold costs about the amount it takes to get it out of the ground. Same with oil, copper, iPhones, whores, cocaine, apples, oranges, fish, widgets. Similarly, a bitcoin will find its value at about the amount of energy/time/knowledge/opportunity cost that it takes to produce one.
I can't believe that anyone would even dispute this. It's just economic reality. 'Money making machines' don't stay 'money making machines' for long.
PS. I'm not a miner. I bought my BTC.
The difference between bitcoins and gold and other products is that it does not matter how many people mine bitcoins - the supply of bitcoins is constant (up to minor fluctuations and assuming that the computing power of the bitcoin network mostly grows), the algorithm adjusts the difficulty to the computing power of the network so that there should always be about 50 new bitcoins every 10 minutes. The price is relative to the supply and demand and in normal circumstances the supply depends on the cost and thus cost influences the price. But it is not the case with bitcoin.