The ocean analogy isn't such a far stretch either - the increasing levels of pollution and emissions from container traffic, using a particularly dirty fuel and an industry that flushes tanks and oil rich pollutants in international waters has an impact on water quality, fish stocks and other ocean life. Roads are a subsidy on cars as they are paid for by general taxation rather than specifically on vehicle use.
Those externalities should all be priced in to discourage impactful behaviour, and encourage truly sustainable behaviour, on the sole viable planet we currently have. At the very least we can make a poor choice knowingly.
It very much does have actual cost, just not today or tomorrow, so it's a bit harder to calculate.
If I break your bike in the middle of winter, the cost won't actualize until spring when you would have used it, and instead have to pay for the bus. So sure, it's not a Q4 cost, but it is real nonetheless.
No, that's absurd way to put it. It's like saying that shipping industry receives trillions of dollars of invisible subsidy due to not having to rent the ocean water the container ships float on. Yes, if oceans didn't exist, shipping would be quite a bit more expensive, and you can even do the math and put a number on that, but the fact is that if you tried to "divert" these "invisible" subsidies from shipping companies, and taxed them for the trillions of imputed income, you'll soon find that those trillions do not line up shipping companies pockets.
The only reason to call it "subsidy" is to imply that the companies are "unfairly" benefiting, but unless these externalities have actual cost to the economy instead of just imputed carbon/water tax, you'll find no resources to divert.