Graph Search - a facility allowing users to find out about other members' activities on the social network
External website tracking - monitoring members through the Like buttons embedded into third-party webpages
Big data analysis - the ability to gain insights into Facebook members' by data-crunching the billions of interactions people have with the site every year
Those arguments don't seem very compelling. The internet is driven by ads. Companies which don't optimize their ad pipeline tend to die. The best way to optimize your ad pipeline is to collect data and then act on it.
Where is the line between optimizing an ad pipeline and violating privacy?