Of course they have an actual cost the economy. In health impacts from polluted air, in impacts from changed climate, increasing intensity storms, floods and such. There's been more than enough studies showing impacts.

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.