My understanding is that Facebook doesn’t actually sell data to advertisers. By this I mean you can’t go to Facebook and say, “I would like to buy data for 10,000 18-24 year old males in New York City, how much?” Instead you say, “I have an ad I want to show to 10,000 18-24 year old males in NYC, how much?” Facebook then handles serving the ad for you and sends you data about how succufull your campaigne was, when people click on the ad and visit your website you obviously can collect data from them there. This is subtle difference and one I think few people have been articulating, probally in part because it makes you sound like a shill for Facebook.

This actually makes more sense finically for Facebook, if they did the first thing people would only have to buy data once, and worse they could resell the data to third parties decreasing Facebook’s control of the market. Instead by retaining control of the data Facebook can charge an advertiser for every ad they show, making more money. Ironically this also better protects peoples privacy because Facebook isn’t actually giving the data away.