"While we have an ongoing review of our targeting options, we clearly need to do more," Osborne said. He added that Facebook was "taking a broader look" at both its policies and its ability to detect categories.

Some of the categories stayed put, typically because they overlapped with categories that have innocuous meanings.

The company does use human oversight to verify its ad categories, and in summer 2018 pulled 5,000 categories that could be used for discrimination. It already blocks targeting based on some obvious terms. However, that method clearly left gaps -- and there's a concern that racist groups might search for terms Facebook hasn't banned in order to target potential recruits to their cause.