The devil is in the details. Often it is very hard to price the negative or positive externalities. And sometimes companies are far and away in the best position to make an estimate of this.

For example, if you believe that Facebook played a large role in electing trump and that trump is bad how would you even begin to price such a thing. If those things were both true how could we ever find out.

Purely shareholder value is an overly narrow way of looking at the world or making decisions.