It seems that if you were not hired after the company viewed this private information, it would be very hard for the employer to avoid claims of discrimination based on what they could have seen.
I don't see how your marriage status, parental status or sexual preferences could otherwise be disclosed during a regular job screen process.
However, the employer doesn't have to "confirm membership" of any status in order to open themselves up to credible legal action. All they need to do is give the impression that they were given some information about protected status, and their "no hire" decision becomes easily suspect.
It would be hard in a litigation setting for the employer, after viewing someone's Facebook data, to be able to cite and document exactly which pieces of information influenced their decision, and which pieces of (discriminatory) information did not influence their decision.
This isn't something that a smart employer would want to open themselves up to. It seems like the actual cases cited have all been rather limited in scope (checking prison guards for gang affiliation).
