Not sure how the facebook app integrates with the contact list, but isn't it only a projection of information that facebook servers publish? I.e. it's not "your personal contact details", but rather an entry that you accepted as being presented by facebook?

It would be disturbing if they changed an existing entry that you created yourself, but if it's only an entry bound to an external (facebook) account, I'm not sure it's that bad. Which one is it then?