As many have pointed out, Google could handle this in their end and avoided pissing off a small but well defined group of users/developers. My guess is that they decided it wasn't worthwhile because they have some privileged ideas about the direction web marketing will be taking in years to come. As user behavior tracking and analysis techniques become more refined, ads won't be needed as much as they are now. Instead, ads will be placed in high impact areas/sites, and the intel to decide who sees what ads will be acquired even from sites with no ads. Better UX, deeper knowledge of users, simpler monetization strategies for publishers. Sure, it will be even more invasive of privacy, but it won't _feel_ that way to most users. This will require heavier use of NLP and ML, two things Google devotes a whole lot of time and money for.