I understand the theory of externalities. I certainly understand that it’s difficult or impossible to know all costs to all parties for some good. But that does

I understand the theory of externalities. I certainly understand that it’s difficult or impossible to know all costs to all parties for some good. But that doesn’t mean there aren’t pretty clear examples, like burning fossil fuels. It certainly doesn’t mean you can dismiss any mention of externalities simply because they are complicated. Some people are bald. You talk about how certain goods are immensely beneficial to society, but that’s not sufficient to claim there are positive externalities. Your example of a road being used by a store that you buy from is a poor example. Those transportation costs would simply show up in the cost of the stuff you buy (disregarding government subsidies for roads, of course, but that’s a separate issue).