Your suggestion amounts to using Facebook as an infrastructure, not directly using their user-facing services. The problem is that alternative (and open source) infrastructures have been developed, but nobody had the UI that Facebook has so people used Facebook anyway.

Some like to argue that alternative infrastructures failed because "my friends weren't there so I couldn't use it" but that chicken-and-egg problem does not exist in small tight communities such as makers and startups. Yet, all those groups stayed on Facebook anyway even after trying Diaspora et. al. The common reasons were UI and features.