I think it's bull that employers often fire people because of what is on their social media.
This, I agree with, generally speaking. It's petty for employers to facebook search employees or potential employees. And it's extremely petty when employers try to tell employees that they cannot so much as post a venting rant about a bad day at work, etc. Too many employers nowadays have lost all concept of an appropriate work/life balance. People don't live to serve their employers, they maintain jobs to serve the needs of living. More companies and managers need to remember that.
However, I do think there can be especially egregious examples where a company takes objection to an employee's social media behavior. The PR executive that made sensationally racist comments mid flight about her trip to Africa is a good example. In my line of work, there are many hotel companies who expressly forbid publicly sharing information about high profile guests. These are behaviors that speak directly to a person's ability to perform the vital functions of the job, and strike at extremely important and fundamental values, the violation of which is highly egregious for the employer.
None of anyone's business and employers should not have a right to even see them.
As much as I dislike employer snooping into social media, most of the time I also tend to have little sympathy for people who fall victim to it. Social media is not an inherently private place. You're the one who is choosing to share your words and pictures online for all the world to see. People need to learn how to adjust their privacy settings accordingly. If people choose to use social media platforms that don't afford them the ability to limit privacy, then that's a choice a person makes and they are responsible for the consequences. For myself: 1) I never add current work colleagues to my list; 2) I cannot be found in a facebook search by people not already on my friends list; 3) People cannot view my pictures, posts, or my friends unless they are on my friends list; 4) People cannot tag me or check me in without my approval. Even if an employer managed to find me on facebook, they'd get stonewalled trying to see anything more than my profile picture and my cover picture. It's not at all difficult to set good privacy settings, and people can't be bothered to do so don't get my pity.