Facebook is where the clueless people are. Unfortunately, I love quite a few of those clueless people - so I join them where they are.

When all your friends decide to meet at that fake corporate fac-simile of a cliché pub, you go there too because you like your friends and might meet some nice girl there too. You may suggest a place with beer that does not taste like llama piss, but you drink that beer with a smile anyway because in the end it is all about people, even with stupid UI, satanic EULA and sprawling ads.

I agree with the gist of your sentiment, but I wouldn't call them "clueless" - maybe unaware, or unconcerned.

"HN, Twitter, Reddit, Google Groups, and Usenet"

Many of these examples tend to be online communities that share the same interest as you. Sure, you can probably configure your own Google Group (i guess?) but who's going to do that?

Facebook is mostly used by people to keep in touch with their offline community - their real-life friends.

Because life ?

Sounds like you're happy where you are. Plenty of people's social presence is only Facebook, so the only way to keep abreast is through it.