The debate of "unfriending" on Facebook

So a friend of mine was on Facebook (not complaining) but merely stating his disbelief on being "un-friended" by an acquaintance. So this resulted from some "heated" political discussions and clearly they both saw things differently.  In this day and age I am under the impression we are all entitled to our opinions (some will agree and some won't). I think it's sad that a dialogue can't persist, in spite of each others differences.

What would make someone "un-friend" over a political conversation?...obviously, a nerve was hit (my opinion), maybe my friend made them doubt what they so strongly believed or brainwashed to believe and was now forced into seeing the light. No one likes to be told they are wrong but to be proven wrong is much worse. I'm just throwing reasons out there, I obviously don't know why he was "un-friended".
I personally think politics, religions etc should not be discussed in a setting such as Facebook.

Hmmm, I wonder if I should check to see if anyone "un-friended" me.