In this case, the customer is the advertiser, Facebook is the broker, and the users (and their data) are the product. With its recent action, Facebook is clearly saying "the customer comes first."
> Or one that says that people who visit free sites shouldn't complain?
Facebook may be free in the sense that I'm not giving them my credit card number and they are not charging me a monthly monetary fee, but the price of admission onto Facebook is your private information. Even if you don't enter anything in your profile, your friends will start to form the links (by searching for you and sending friend requests (even if you don't accept them) or tagging your face, etc.) that any marketing person pays big money for.
Facebook is not free and the customer is definitely coming first.