Practical Difficulties of Eliminating Externalities

As Alison Butler does not fail to address in her article, eliminating externalities can be extremely complicated.  Assigning property rights seems logical in simple examples, as we hope that principles of the market will create an equilibrium between private and social costs.  In practice (using the chemical plant upstream from a town example), however, it seems like it would be very difficult to A. quantify environmental damage with a dollar amount (how much should the firm pay the town), and B. gauge the opinion of a community regarding the optimal level of pollution (what level of pollution should the town pay the firm to reach).  As Butler notes, this all becomes increasingly confusing as these problems become international, as the natures of different nations inherently predispose them to accepting different environmental practices and policies, making the formation of international agreements on these issues much more difficult to obtain.