Externalities are incredibly difficult to identify or quantify, and whether they are positive or negative is often a subjective judgement.

In sum, technologies generate significant negative externalities. More importantly, patented inventions-which enjoy government-granted exclusive rights-also generate significant externalities.114

Of course, it is exceedingly difficult to identify and measure the full scope of externalities associated with any invention.115 While some externalities are obvious, others are quite attenuated from a particular invention. At this level, characterizing an effect as a negative externality is a policy judgment akin to the notion of proximate causation in tort law. Depending on one's judgment, the negative externalities of Facebook may include work hours lost to procrastination, harms to political discourse, and widespread feelings of ennui from seeing one's Facebook friends lead seemingly glamorous lives. Additionally, characterizing negative externalities can be highly context specific and subjective. Video games and the consoles that play them are certainly economically significant technologies. But are billions of person-hours spent playing video games wasting time and desensitizing people to violence, or do they provide beneficial amusement, excitement, and education?116 Finally, as should be clear, even if one can properly identify negative externalities, it is very difficult to quantify them in any practical way. It seems doubtful that one could translate the harm from ideological polarization into a dollar amount for purposes of imposing a Pigouvian tax on Facebook's patented filter bubble technology.117