Culturally we seem to be moving increasingly towards echo chambers as we are losing the social skills to be capable of engaging in dialog without immediately collapsing into emotional rants.
Think today's politics are divisive? Look back to the mass social unrest and violence of the entire 20th century (or farther, at all of human history). This is not a new phenomenon, and there's nothing unique about Facebook, the Internet, social media, or technology.
No. Facebook (and web echo chambers in general) are dramatically different. Because the available online population is so much larger than a physical community, narrower and louder echo chambers are possible. Back in the offline days echo chambers were more self-limited and internally more diverse, because the smaller pool of possible members meant too much exclusion would make the group too small to be sustainable. Now, every crazy fringe idea can have a Facebook group of 500 active members egging each other on, and use targeted ads to easily suck in every susceptible person.
CNN documented that the Russians pushed propaganda on both sides, once having helped plan a protest and a counter protest at once. Their plan to disrupt democracy is very much helped by echo chambers.