A computer or a home that uses more energy has externalities for others that certainly aren't covered by your electricity bills alone. Taxpayers pay for new power plants, everybody pays for emissions, etc. Almost everything has externalities that aren't fully accounted for in the sticker price, because it would be insanely complicated to do that kind of accounting, let alone do it in a way we can all agree on.

If you think the math for cars is uniquely bad, I think that's a reasonable position, although I suspect it's pretty myopic. The externalities of cheap consumer goods from China, or of a clothes dryer or an AC unit, are pretty terrible too.

The math aside, there is a huge risk to this sort of hyper-rational accounting. It's probably not cost-effective for the society to medically prolong the lives of people over the age of 50. There are many squishy, hard-to-parametrize overriding considerations for policy decisions, and if we accept it for our lifestyles, we should probably at least try to understand what they are for other lifestyles too.