https://phys.org/news/2018-07-zuckerberg-holocaust-deniers-wont-facebook.html

After the remarks caused a backlash on social media, he was forced to backtrack, saying if any post advocated violence or hate against a group, it would be removed.

The controversy began when Zuckerberg provided an unprompted example of Holocaust deniers to Recode host Kara Swisher to make a point about allowing hoaxes to be published on the site.