The mistake you, and most others that come to this conclusion, make is that bubble thinking existed long before FB and will exist long after FB. Hell the idea that you can interact with people outside of the hundred of so people that live in your small town is relatively new idea in most of the US.
The difference now is that outsiders can observe the tribal thinking. Sure it's sad the Internet didn't deliver on the revolution of the 90s interms of bringing us all together; however, I think the idea of being connected to people is only going to increase in importance as the global workforce becomes more and more mobile and bonds become decoupled from geography. I don't think it'll be Facebook (at least in the model that exists today), but it's difficult to deny the massive demand for that kind of product that has been the fire driving the company forward.
This isn't true though, Facebook has special filters to remain friends with people and just block any posts from them. This means there is no negative feedback loop when you're posting trash because everyone who disagrees will eventually unfollow you.
In real life, social interactions expose you to people with different viewpoints and social decorum forces you to listen/engage for at least some modicum of time. You couldn't selectively ignore people when they were talking to you. If you behave like an asshole, people who disagree eventually stop interacting with you and you quickly notice that (negative feedback).
That's a major assertion without much back it up. I have no data either, but anecdotally I'd say you're probably wrong. I grew up in small town america, you don't get exposed to different view points, and if you do the common action is to just deal with the friends you have; there's not much else (this is why the bubbling on social media happens so readily; it's what people are already doing). Also I hesitate to assign people "unfriending" as a negative feedback loop. You get no notification you've been unfriended, and there's no mechanism to indicate why the action took place. If anything it might be reaffirming?
I'd also posit you're underestimating the value of a network of weak connections. This is especially true under the idea that most people will work some place different than where they grew up; reconnecting with friends that drift toward the same hub is a powerful tool.
The difference now is that outsiders can observe the tribal thinking. Sure it's sad the Internet didn't deliver on the revolution of the 90s interms of bringing us all together; however, I think the idea of being connected to people is only going to increase in importance as the global workforce becomes more and more mobile and bonds become decoupled from geography. I don't think it'll be Facebook (at least in the model that exists today), but it's difficult to deny the massive demand for that kind of product that has been the fire driving the company forward.