I've looked at Dorothy Howard's Pew polling numbers. There are more recent surveys than the 2013 one, although the results are similar.
On social media use generally: http://www.pewinternet.org/files/2015/01/SurveyQuestions.pdf
On where internet users get news: http://www.journalism.org/files/2015/07/Twitter-and-News-Survey-Topline-FINAL1.pdf
The survey universe is pretty small. 2000 US adults were interviewed; half of those were via cell phone. 75% of those adults self-identify as internet users. The percentage of US adults (adjusted for internet use) who use FB is 71%, which seems high, but of those only 45% visit several times a day. A significant percentage uses sites other than, or in addition to, FB: Twitter (23%); Instagram (26%); Pinterest (28%); LinkedIn (28%), with smaller numbers visiting those sites several times a day.
As for where users get their news, 40% of Twitter users say Twitter is "an important way I get my news" and the same percentage was found for FB users.
This may be a compelling argument to be connected to *some* form of social media but I don't see why it has to be Facebook, especially given all the negatives ZI is reminding us of. Howard's lead statement, "Facebook is so widely used that opting out constitutes an act of defiance of the norm," is essentially an advertisement for Facebook and is thinly supported statistically. Again, I realize we have some heavy Facebook users on the Rhizome staff but I don't think it's fair to couch this as a popular mandate or say that Facebook rises to the level of a "public utility," the way the telephone system was 40 years ago. There are too many other options: you should be emphasizing those.

Also, Ripps has said here on Rhizome that "the comment thread was friends only and i did not expect excerpts that fit the [AFC writer's] narrative to be screengrabbed." This was not a case where the post was "shared with journalists and used for publicity purposes."

They may both have been emotional. My point was the Facebook argument was "secondary" information and the Livejournal documentation was the "primary" artwork. This also applies to whether Ripps was using the Facebook account for publicity.
A good art critic reviews, say, a painting. A bad or lazy one reviews the press release or artist interview, that is, "attacks the hype." A more scholarly approach to writing is to consult secondary sources only when the primary are ambiguous or incomplete.

In the case of Paddy Johnson's unpermitted use of Ryder Ripps' Facebook screenshots, there was no "strong public interest argument" to share the posts. His art was not made with public money. It was mostly lazy art criticism on her part. His "Art Whore" piece as documented on Livejournal was difficult to attack on its own terms so she relied on a private argument he had with an emotional Facebook commenter to provide extraneous text that undermined his project. (I'm saying Paddy but it was her subordinate Whitney Kimball.)
Artists violate contextual integrity all the time. We ask a bit more from our record keepers.

If you have a substantial time investment in Facebook and put a lot of content up there, you might want to think of it as a public utility. I believe the web is large enough for people to have a public presence without being on Facebook, and this "utility" is sand you're building your castles on. If you're stuck in the sandlot and want to organize with your fellow castle owners to make the ground less toxic, fine, but I'll always think it's kind of silly.
Another problem with the public utility analogy is that those entities are government-granted monopolies and are subject to public oversight. If you have a problem with the power company you have a government board that hears your complaints. Pressure comes from without, not within. Whereas Facebook is this weird voluntary addictive thing that takes over people's lives and most of them don't know how they got there (to continue the smoking analogy). We try to offer those people alternatives, we don't encourage them to organize as they continue to buy tobacco.
More on the "contextual integrity" issue in another comment.