I've actually given this subject quite a bit of thought. To me, it's no big surprise that employers started using Facebook to vet potential employees. I can see how that would be beneficial, but I can also see it looking too invasive. "Indeed, Jeff Vijaunco, vice president of world-wide talent acquisition for Adobe Systems, Inc., said that in focus groups, prospective job candidates were sharply averse to being contacted though Facebook for jobs."(WSJ). I personally see no problem with a company looking at a potential employees Facebook page. I would be lying if I said that I've never scouted out a photography client before. What kind of person are they? Do they have the same interests as me? Are they professional? You can really tell a lot about a person from their social media. Good and bad. This is why I believe that if you put it online, you should be ready to face the consequences.
Now, people will always argue that this is an invasion of their personal privacy. To that, I say: no one forced you to have a social media presence. The government does not control Facebook, and you took part in it willingly. Also, many people have "keyboard courage" and feel that social media is their personal soapbox, and will often say things that they would never in a million years say in an actual public setting. No one in normal society would announce their political, anti/pro religious, homophobic, raciest, etc. thoughts to the world. But since they are online and not in "real life", they say whatever comes to their mind. Believing there are no consequences.
Now, to play devil's advocate: the ONLY time I can see a social media investigation infringing on someone's personal right to privacy is when a person is unknowingly photographed or videotaped and added to someone's social media page. Here is the scenario that comes to mind: an elementary school teacher is photographed drinking heavily and participating in drunken shenanigans at a bar, then tagged in the photo by someone else (or is recognized in the photo without any connection to his/her own social media page). That teacher is then fired for acting inappropriately. Sure, that teacher didn't deserve to ousted in that way, and they didn't ask for that to be made public. However, it happens. Often. So should your private life be considered separate from your profession life? If you aren't on the clock, should behavior like this be used against you?
Reference:
"Recruiters Troll Facebook for Candidates They Like." WSJ. Web. 26 Feb. 2016.
Reference:
"Recruiters Troll Facebook for Candidates They Like." WSJ. Web. 26 Feb. 2016.