Facebook as an institution of social credit

The Facebook dating service thread references using a Facebook profile as a way to judge client trustworthiness, and limiting interactions to people with said profile. While Facebook participation is voluntary for most people right now, if it increased to the point that hiring companies could limit candidates to just Facebook users and still have a sizable pool, would they have any incentive not to?

Is there an upside to preserving a society with no social credit scorekeeping?