I've never unfriended anyone for politics specifically, and have only unfriended three people. The first was a poster here who made creepy comments on my photos, I don't think he posts here anymore. I should have looked at his picture when he sent me a friend request, but I just looked at the mutual friends list and thought, "Okay." The first thing he did when I accepted the request was to go and look at all my FB pictures and start making comments, and it just creeped the hell out of me. The second was an asshole who was just a bully, I think maybe a friend of a poster here. The third was my cousin's husband. They are in a cult (a literal, shave your head, crazy cult) and he specifically is mentally unstable. He went on a rampage on my wall once after I spoke badly about Jenny McCarthy's dangerous antivax message. He started posting crazy, harassing shit on things I'd posted months before, so I had to block him.
I've been unfriended twice as far as I'm aware, and both times surprised me and seemed like major overreactions. One was the mother of a childhood friend. She had posted some meme about honey and herbs curing diabetes. I gave a thoughtful, unaggressive response basically encouraging her to research such things and expressing concern about the dangers of that type of meme, and she freaked. The second time was almost the exact same situation: someone posted a meme with disinformation, I politely corrected it, she freaked and blocked me. After it happened the second time I was worried it was me, but others confirmed that my responses were not confrontational, and that blocking seemed an overreaction.
It seemed to me those were perfect examples of people who want to live in echochambers, and it's a shame. At once, I think it's important to have the ability to unfriend and block people because they can be abusive, but it's sad when people use the tool to just bury their heads in the sand. Though more of my friends are liberal than not, I have friends across the political spectrum, and across the religious spectrum. There have been times I've felt the urge to unfriend someone over something they've posted, but I've refrained because I think it would be a shame to lose their points of view, even if I disagree with them, and there have definitely been times that they've posted comments, ideas, and links that made me reconsider my own opinions.
There is this one lady I'm FB friends with that I get the urge to block at times. She's a Redskins fan. We had a polite and brief debate over the team name, and it was a perfect example of someone rationalizing a belief that contradicts their general views: she tends to be very empathetic and compassionate, but she can't get over herself when it comes to the fucking team name. It's not fun to see racist slurs pop up on your wall, and it's even worse when you know it's someone who should know better.