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Here's a great example. I go on a canoe weekend with a bunch of old friend each year. Some years it has an upwards of 100 people attending. I know about 10 to 20 people, including the hosts, very well. The rest are either acquaintances, second connections, or friends/family of the hosts.
Everything gets done via a Facebook event because it's the easiest way for the hosts to communicate with a group of 100 people. A few people "refuse" to use Facebook so all communication with them about the event has to be done on a secondary channel. Sometimes those people accidentally get left out of important notices. It's nothing malicious, just the hosts having jobs and busy lives and forget about a few odd ones out.
I haven't used Facebook for years and it has not obstructed my social life in any way.
But if that choice is harder to make, the world is probably worse. Its that more people on facebook, feeling its a requirement, is a bad thing.