It's all part of the interesting psychology that people manifest while participating in this pseudo-public space called a Facebook profile. It is the digital equivalent of a podium on a stage that has flood lights obscuring your view of the audience. You know that people are there because you hear them but you can't exactly see them all (analog of not knowing who sees what you post or reads it) this does an interesting thing to people. First, when challenged while on their "stage" they are far more likely to react with a defensive posture on many subjects that in reality they would be for more reasonable discussing. I've been perplexed by the harsh tone some people I know on FB have taken that seems like a contrast to the character of them I know in person...that said, it is easy for this magnified personality and feeling of self importance, coupled with the fear of "public" shame to really lead people down a path of paranoia.
If you do draw their ire, they may feel sufficiently offended to de-friend. There was an FB friend I had on my list for about a year, he was a smart computer programmer from Canada. I friend requested him because he was good at defending his self logically for the most part but he would never admit being wrong if pushed to that logical end. He also had a habit of asserting his greatness in programming out of the blue, we had many debates regarding Engineering and programming where I would enjoy mildly ribbing him over one statement or another (we were fully in super pedantic mode and though he didn't slip often when he did I made him pay for it)...but it seems he never liked it.
Finally a couple of months ago I posted an article about Star Trek Enterprise (the tv series now off the air) he took great offense at the fact that I interpreted the way the series ended in a different way from him...so much so that soon after that discussion (which was cordial outside of his making the accusation that he knew more about Star Trek than me...but failing to actually show it) I found I couldn't view his profile. He had defriended me over a Star Trek discussion! So I say good riddance to any one that takes themselves so seriously that they expect to always appear correct in every interaction that happens on their profile and feel slighted at being censured in this pseudo public forum. It is a delusion of grand audience that magnifies existing quirks in personality to ugly viewable size...I like it...helps us separate the horribly included stones from the diamond quality friends we ideally would all like to have!
So when you are next on FB do a little observation of your friends responses to various statements online as compared to how they would react in person. How big is the gap? I think the difference hints at the level of delusion of self importance that person has...hmmm...now if only there was a way to capture this delta and exploit it. *grin*