So the reason you can’t think of any is because no economic activity exists with out them.
But externalities can both be positive or negative.
In my circles we actually never use this word because it is basically just a fancy way to say exploitation that makes capitalists feel good about them selves.
Exploitation is orthogonal. You can have internal or external value exchange that is exploitative. You can even have positive sum transactions that are exploitative.
It must be exhausting having conversations in your circles if you change the definition of all the words…
As opposed to something like heliocentric solar system theory, where you don’t need to play word games to prove the counter. You just need to observe and collect data and use the same words to come to the correct conclusion.