As I say in my 50 second CBS News Radio Eye on Tech segment (click below to listen), Mark Zuckerberg said several times during his Senate testimony on Tuesday that Facebook never sells user data to advertisers, but he didn’t explain why that wouldn’t be in Facebook’s business interest.
By keeping the data and selling your eye balls, Facebook can keep the advertisers coming back, making money each time. If they sold your data, it would be a one-time sale and there would be no repeat business. Not selling user data isn’t just ethical, it’s good business.