Re: A thought experiment
If Facebook, etc. stopped overnight, the others would step in to fill the gap. It wouldn't take much. There are already plenty of other platforms out there. There'd be a bit of wailing and gnashing of teeth, but, hey ho.
I left one post on Facebook, to let people know why I'd left. I went back to check, and that post had been deleted... but not by me. Also, if you try and browse my facebook page, you'll see a facebook error. However, to me, it looks like all is fine and dandy.
Also... I spent some time repeatedly going through my history, deleting all the posts. Returning to check, some months later, one of those old posts had reappeared. Funny that. Also, you can't block Zuckerberg.
You know real friends... who you can not talk with for years and when you do, it seems like it was only yesterday that you were chatting over tea and cake... well, Facebook doesn't value those friendships. If you don't interact with someone on a regular basis, it drops them from your feed.
And there's more where that came from.
Facebook is a poisoned, feel-good chalice that is doing us no good. I found myself facing posts simultaneously from friends, one whose cat had just died, and another was celebrating an exam win. I found myself unable to empathise with them both simultaneously... and ended up putting on some kind of emotional mask so I could chat with them... and it felt dishonest.
The sooner Facebook dies... the better... IMHO.