This is exactly what I find unconvincing.

If it creates a filter bubble how can it then increase tribalism and polarization?

I'm honestly confused by this comment. Being stuck in a filter bubble and increased tribalism/polarization seem like two things that rather obviously correlate. I don't really understand how that's not obvious.

Where does this tribalism and polarization take place if not online? Do you have any evidence of changed patterns in "real life" with that regard? So if Facebook keeps people in bubbles so they never get exposed to other views how do you know they are more polarized if not using social media.

The echo is louder in your bubble Facebook creates for you.

Not sure what that even means.

Let’s say you’re my father in law. Let’s also say you get most of your news from your biker friends in their 50s and 60s. You might then be surprised to hear that the border wall has not been funded, that Trump does, in fact, not make us appear as the leader of the free world. That illegal immigrants are not the reason for soaring health insurance premiums.

These are problems you face when you interface only with people who share very congruent values and obtain their news from the same source. If Facebook uses Skinner Box techniques to keep you on the site as long as possible, it’s not interested in outcomes that are good for you but might make you leave, like challenging your beliefs and values.

Yes but that's not what's going on on Facebook. You aren't isolated like that.

It's an oversimplification of how the algorithm actually works as there are plenty of non-political interestest involved too.

Respectfully disagree from my anecdotal evidence. Someone sharing politics you don’t like? Unfollow or unfriend, leaving content in your feed that you want to see, reinforcing your beliefs regardless of the truth/facts.

That is in contradiction to my anecdotal evidence and having done my share of research with regards to FB feeds in my line of work.

Luckily for us, social scientists have done in depth research on this issue and published the results:

http://education.biu.ac.il/files/education/shared/science-20...

Conclusion: People are extremely aligned to viewpoints, reinforced by their friends, however they are less aligned than if they STRICTLY consumed media from their own viewpoint because they have some cross-cutting issues.

"... our work suggests that individuals are exposed to more cross-cutting discourse in social media than they would be under the digital reality envisioned by some (2, 6). Rather than people browsing only ideologically aligned news sources or opting out of hard news altogether, our work shows that social media expose individuals to at least some ideologically crosscutting viewpoints "

You seemed to miss the part about more cross-cutting...than envisioned by some (2,6)

Key relative measure there and worth reading into more depth.

Not missing anything just giving a more nuanced picture than what you seemed to suggest.