This is like saying my car's engine uses oil as lubricant, not as fuel. It's true, but I still have to change the oil every 5,000 miles. So I can still calculate the cost of oil changes into each mile.

Since transacting Bitcoin securely is the utility of the network, just as moving around is the utility of a car, it seems quite fair to judge the energy consumption of the network in terms of energy expended per transaction secured.

It's quite different: the energy represents the market cost of securing the network. The value of the network supports that cost otherwise nobody would be performing mining.

If this were taxpayer supported I could understand the objection, but the people buying the energy to run the system are doing so as a commercial activity to make a profit. How is this commercial use of energy inherently worse than other commercial activities?