Externalities always felt glossed over in economics. So yes this business will ruin the river for everyone but please direct your attention to this chart and look at all that producer surplus!
https://www.law.uchicago.edu/sites/default/files/file/coase-...
Leaving aside the fact that the Economics prize isn't actually a Nobel Prize, topics which historically haven't been given enough attention are exactly where the highest impact research takes place.
If externalities had always received the attention they deserved, Coase would have never received his prize, because his work would not have been so important.
I think its safe to say that externalities are not, and were not, an ignored sector given more than a century of serious work, and the fact that it is covered in any intro level Econ course.
Inside of economics, they have more than 130 years of work, and are taught in any intro class.
If your argument is that we are bad at correcting for them, then yes. But that is different than not considering them.
Climate change has been discussed for well over a half century, yet one of the main priorities of the current administration has been to hamstring renewable energy and promote coal and oil. I think it's pretty fair to say the issue is being ignored.
The consideration of externalities that don't impact the bottom line is so alien to the real observation of the rites of capital that it might as well be written on the inside of a particularly boring rock in the oort cloud.
It turns out that for many purposes friction and externalities are small enough that they can be ignored for most purposes.
Physicists and Economists are very aware of the tradeoffs.
Although, I am all for a data driven world but somehow it is my opinion that we have ended up with the worse of both as combined with the goodhart's law, this measurable thing just ends up somehow getting manipulated for short term gains over real long term damages.
As is your case in the example, the business will ruin the river for everyone having severe damage both culturally and I think financially as well given downstream effects of all people depending upon that river.
But the business has externalized the losses to the people and the people have externalized the responsibility of the river to the government and the government believes in absolute free capitalism! (or sometimes the businesses give the government some money in the pocket ie. corruption. "Cost of doing business" they said.)
I am not against capitalism itself (that Adam smith proposed) but capitalism in its current form is definitely something... and surely some if not most of us might agree to the fact that system isn't working as intended (well not working if it was intended for us ie.)