I agree that the ethical discussion is likely the paramount concern here and should be discussed, but the code they're using floods the global namespace which in theory could actually degrade service for end-users (by potentially breaking commonly visited JS-powered sites that happen to use globals of the same name).

Its worth pointing out that it would take minimal effort to make this code not suck as much (wrapping it in a closure for a start). IMO it gives more context to the initiative on Comcast's part. No time, effort, or care was put into considering the ethical implications of this practice nor its practical effect on the end-user.