Did you know there is a secret mailbox on Facebook? I do, but I forgot about it for a long time. It's called the “message requests” inbox. You don't see it right away, but it's there if you look for it.
These are messages from people you are not friends with, hence why they're so hard to find.
One reason I mention it is because I accidentally stumbled upon it the other day. In it, I found a message from nearly a year ago from someone I knew back in college. I won't mention his name or the content of his very long message other than to say that in it he said he “had to” unfriend me because he disagreed with a politically-charged Facebook post I can barely recall writing at this late date.
What got to me wasn't the fact that he unfriended me. (We apparently weren't that close because I hadn't noticed his updates missing in all that time.) I'm “friends” with people on Facebook who I haven't spoken with since elementary school who I assume are unfriending me for one reason or another pretty much constantly. What was weird to me was the idea that he “had to” unfriend me because he disagreed with me on a political issue. That is utterly absurd. This is not a “have to” situation. Also, the impulse to tell someone you're unfriending them for any reason is just plain odd to me.
Unless there is a compelling motive involving reputation or safety, I am generally against blocking or unfriending people on social media over simple political disagreements. It really gets nowhere in the effort to foster greater understanding of viewpoints different from our own.
I find Facebook to be the most obligatory of the social media platforms. I feel the need to be at least somewhat connected to close family and friends there in a way no other service does. Added to that is the fact the main enemy I fight against on all platforms is the concept of the feed. This is the algorithmic firehose which sprays pre-selected updates in a non-chronological order at users.
My main advice to anyone is to pare the feed down as much as possible.
Is there, say, an uncle posting offensive memes all day? Don't unfriend him. Just select the option next to the post saying you want to unsubscribe from their updates. This saves you the awkward conversation of explaining why you unfriended him at the next family gathering, and preserves the illusion for them that you're receiving everything they put out into the universe.
I champion this method because there are times, however sporadically, which have nothing to do with the day-to-day posts we create on Facebook. I've had lovely one-off interactions over specific topics with people I grew up with who I'm still friends with on Facebook, who I forgot I was friends with because I unfollowed their posts. Because I wasn't inundated with their constant updates it gave me space to remember what we shared in the first place during the rare occasions we had something of substance to say to one another.
You can always search for people you've unfollowed on Facebook by name if you really want to find them for some specific reason. If you take the extra step of unfriending them, however, you're denying your future self that option.