Externalities are a myth. Nothing is External. It is all internal to someone or something.
The word Externalities was made up in some boardroom somewhere as a way of saying:
"It is not on us. Not our problem. Someone else will take care of it. Out of sight, out of mind."
It is like the common term used in accounting: deferred maintenance. That is an oxymoron. It is either maintained or unmaintained. "Deferred" means we will not maintain it and let someone else do it later. Kick the can down the road.
What does deferred maintenance of the planet look like?
Probably a lot like today.
What Legacy are we creating for ourselves?