I'll push back against this. It seems to me that Facebook makes it more challenging for you to filter through that bubble. Their algorithms are tailored to get me to engage with the site and keep my session alive as long as possible. Not surprisingly, I'm sure that it will present me more with things that please me -- either things I agree with or people backlashing against things I disagree with -- than not. As a user, it seems it takes an extra level of awareness and conscious work on my part to fight against their ranking algorithms. It does not present to me a snapshot of my social network as it is; it presents me a snapshot of my social network that seeks to maximize its perceived relevance to me at any given moment. That isn't the same thing.

Having said that, I think it is too easy to fault them for this. I'm an educator, and I think the only meaningful weapon against this is educating people on the forces involved. I'm also painfully aware that as I write this, an enormous swath of my fb friends are asking to be "unfriended" by people they don't agree with, so I don't think fb engineers are the real source of our issues in that dimension.