I agree that it was the responsible thing for Google to do.
That being said, is it also responsible to report users who share movies and music files? Right now Google is being selective in what it reports. When does that change?
Google's actions look very conscience-based. It would take an awful lot of resources for Google to actively track down and report widespread illegal file-sharing. It looks like they determined that child pornography is clearly heinous enough to (to whatever extent) compromise user confidence in privacy, as it relates to using their products.
The best answer would be to not engage in illegal activities while using their products.