To "unfriend" someone based on perceived allegiances or something that happened between other people is part of what I call "friendship politics". And while I get it, most of it strikes me as petty. It can sound something like this:
"Hey, I'm friends with someone who no longer likes you. We're not cool anymore."
"Hey, you haven't put forth sufficient time and effort in proving your friendship to me. We're not cool anymore."
"Hey, our group of friends split in half due to someone else's dispute, and you chose the wrong side. We're not cool anymore."
You're valuing your own good will as something that must be earned, and conversely, something that can be revoked. It's not knighthood for godssakes, just be a nice person.
So to anyone who's ever unfriended anyone on my behalf, I appreciate the sentiment, but you haven't done me any favors. I would never ask that of anyone, unless circumstances were extreme. Granted, I suppose I've never been tested. I've never been in a "bad" break up. But as of yet, I take no joy in dissolving friendships.
I take no joy in the sadness of others under the pretense of fairness. That's called vengeance.
And if the word "vengeance" sounds petty and over-dramatic, maybe it's because the concept itself is petty and over-dramatic.