You absolutely can fire people for all those bolded things, as long as your state is an at-will employer, in the US. It's a dick move, to be sure, but it's not specifically illegal.
Race and religion are, of course, covered by various Acts (mostly the Civil Rights Act, but there's a few other protected classes brought in from elsewhere too).
Someone could be the nicest person in the world, if they're lazy, it won't help your company.
Similarly, someone could go for drinks every night after work yet still work good and be efficient.
But let me ask you this, Let's say a person goes out and has a drink almost every night, and makes a picture or two and posts them on facebook. then you have a person who also goes every night and has drinks until they drop, gets wasted, but because of this, they also post 1-2 pictures only as they were drunk the other time. Since all pictures are when they had fun, how do you differentiate between the two? Simple, if the second person didn't post a picture when they were already wasted, you can't. Yet you're ruling both out, aren't you?
Is that unfair? Probably. HR staff want a reason, any reason, to fling your resume into the "do not hire" pile. Anything that flags their attention in a negative way gets you shunted off. HR staff have been known to round-file a resume because they felt the stock of paper it was printed on was too cheap, or because it was in a weird font on colored paper and was annoying as a result.
Skirting privacy settings seems like a plain form of deception, I can't really condone that.
I don't really have any problem with businesses looking at social media as a generality though. I'd happily show a business my Facebook account if they desired; all they'll really are some items linked that I thought were interesting the news, pictures with friends and family, and pictures from duathlons and running races. Some of these include alcohol, but not an inordinate percentage, and I have no desire to work for a company with a sufficient stick up its ass as to use that as a disqualifier.
As for what a current employee can or cannot be fired for, thanks for the correction.
Actually a fair question, what if there are more people named like me on Facebook, you haven't met me in person yet and I didn't use my work e-mail for facebook? What then? Do you take the first person with same name? What if there's a photo of me in my CV, but my profile photo does not have one of me? Then you can't find me that way either. Or do you check all the people named like me?
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Your personal information is given to companies and the companies use it as they see fit, in this case by deciding if to hire you or not. Or this is what they say, we already concluded they do shady things, they lie to you and check you behind your back without your approval beforehand on personal private information, so who's to say they don't use your information for more? Hmm? Who's to say they don't sell it too or whatnot. Who draws the limit? Where is the limit drawn? You don't know, yet you accept this breach of privacy as it's normal. Well it shouldn't and you shouldn't.
I can never agree with companies checking private parts of your online life without a court order. Because it's private.
And I don't know how laws are in your country, but in mine you can be sued even for checking your mate's e-mail without their agreement. When married already. Why? Because it's considered private information by law. And private information can not be breached without an accord.
Oh, do they want to check stuff you made public? Be my guest, in the end that's why it's public.
I find Facebook's official stance on multiple/pseudonymous accounts to be ironic considering that their practices regarding the submission of individual user information to employers are what fuel this countermeasure in the first place.
Selectively choosing those to uphold your company's culture and values is part of what is turning corporations into for-profit cults.
I do not want OP to think that I just think they are scum, but also the good folks at facebook for being so incredibly deceptive. What is the point of having privacy settings at all other than to give people a false sense of security? All of this is why people are growing more and more weary of corporations. They seem to be above the law. Do not get me started on the use of lawyers to write terms of service so fucking convoluted that you need a career in law to understand.
Again, you are not wrong for using the service available. You are just an asshole if you do. Seems that being an asshole is part of being successful in general. Decency is a rarity at the top.
I like sandwiches
Facebook and social media in general is not private and never will be. By definition it's putting your life on the internet. If you don't want it examined by the public, don't leave it out there for them to find.
All this is really besides the point though. All this really does is weed out complete morons. Which is the job of those in charge of hiring anyway. When you assumption is "Everybody lies." All you really prove by browsing online profiles is that someone lied. When there is no online profile or the information matches the supposed lie, you've gained nothing. Knowing a person is a liar is a better position to be in rather than only thinking a person is a liar. The big problem with the latter is that if you assume someone is a liar, but hire them on the basis that knowing someone is a liar, and then treat them based on your assumption that theyre a liar, you run a pretty strong risk of creating a hostile work environment.
You're in part right that a person represents their company at all times, and I must admit youre giving a pretty poor impression of your company if your primary assumption of a prospective employee is that theyre a dirty little liar. If you are constantly finding your employees are liars, chances are you arent vetting them very well.
And thus I give you: MALE contraception!
Or drinking every night even if you do your job.
Or a number of other stuff the OP mentioned.
This is not only about weeding the people who lie, this is about weeding anyone they don't like based on crap ideas. It's like those punks in parks who come to you and say "I don't like you because you looked funny at me".
As far as the Affiliates and Service provides thing, those to me don't really leave them much room for that backdoor practice, at least in the summations they give at the end. "We give your information to the people and companies that help us provide, understand and improve the services we offer." seems to only involve business partners, and what part of that leaves room for "business partners that want to treat us like an internet PI firm using our 'secret' data?" "We and our affiliates may use shared information to help provide, understand, and improve our services and their own services." doesn't really open the way for these practices either. I guess very broadly you might be able to say that FB says that, but it'd be a real stretch and just based on those paragraphs I don't see how it would hold up if they were taken to court. But hey, I'm no lawyer.