Not all unaccounted externalities (if you prefer that term) are of the same magnitude, though. It's the magnitude relative to others that matters.
If say 10% of a city's budget goes to fixing truck damage to roads without at least commensurate benefit, then it's a more important issue than whether .05% went to cleaning up cotton candy after the town fair.
It also doesn't even have to be about tax expenditure. The healthcare cost of using fossil fuels is realized in private spending on treatment for pollution triggered respiratory illnesses, and the economic cost of climate change effect mitigation, which is already being accounted for in business planning.
If say 10% of a city's budget goes to fixing truck damage to roads without at least commensurate benefit, then it's a more important issue than whether .05% went to cleaning up cotton candy after the town fair.
It also doesn't even have to be about tax expenditure. The healthcare cost of using fossil fuels is realized in private spending on treatment for pollution triggered respiratory illnesses, and the economic cost of climate change effect mitigation, which is already being accounted for in business planning.