Facebook employs hundreds of people who read and tag posts. All, not just "public." Readers of your posts are classically external suppliers, and Facebook lets them categorize them to better understand what people are putting on Facebook. You can't avoid this, and Facebook insists that this other major privacy violation just needs it. The team of externals even went back to 2014. Each of the designers who come from India, Romania, Manila and the Philippines sees 700 posts a day.