[irons]

For the purposes of advertising, facebook does not need you to disclose relevant information to anyone but facebook. Advertisers need never come anywhere near that information.

Facebook's whole lever for motivating people to provide that information is so they can share it with their friends. Why would anyone fill out a demographic profile to be kept under lock and key by Facebook for advertisers?

[shadowfiend]

Again, that particular sentence was specifically about advertising. Of course facebook wants you (and you want to) share that information with people other than facebook, otherwise you wouldn't be on the site. The question is whether they then turn around and feed your information to advertisers, and I don't think they do (or that they need to).

[irons]

Advertising is Facebook's reason for being, but this story is about people over-sharing with other people (mediated through APIs). Advertising appears irrelevant, except insofar as it's Facebook's reason for being.

If Facebook did exactly as you suggest and walled off advertisers from all but aggregate user detail, it wouldn't have affected this app, or anyone using similar techniques.