While I'm sympathetic to the argument that the rise of social media has contributed to the absolute degeneration of public discourse, blaming social media as the cause rather than the means strikes me as particularly hollow when measured by previous historical periods of civil unrest. Whatever the actual causes--nascent technological catalysis, changing property relations or elite culture, or whatever the God's-eye picture of its real etiology--this phenomena is recurring throughout human history. Sometimes mobs (viz. mass-movements, factions, parties) form and mobs, like houses, cannot stand divided. Competing mobs become one mob or destroy each other.

Consider this letter from Thomas Jefferson to Edward Rutledge in 1797:

"The passions are too high at present to be cooled in our day. You and I have formerly seen warm debates and high political passions. But gentlemen of different politics would then speak to each other, and separate the business of the senate from that of society. It is not so now. Men who have been intimate all their lives cross the streets to avoid meeting, and turn their heads another way, lest they should be obliged to touch their hat. This may do for young men, with whom passion is enjoiment. But it is afflicting to peaceable minds."^1

Or Jefferson's retrospective of the 1800 election:

"we suffered ourselves, as you so well expressed it, to be the passive subjects of public discussions. and these discussions, whether relating to men, measures, or opinions, were conducted by the parties with an animosity, a bitterness, and an indecency, which had never been exceeded. All the resources of reason, and of wrath, were exhausted by each party in support of its own, and to prostrate the adversary opinions. one was upbraided with recieving the Antifederalists, the other the old tories & refugees into their bosom. of this acrimony the public papers of the day exhibit ample testimony in the debates of Congress, of state legislatures, of stump-orators, in addresses, answers, and newspaper essays. and to these without question may be added, the private correspondence of individuals; and the less guarded in these, because not meant for the public eye, not restrained by the respect due to that; but poured forth from the overflowings of the heart into the bosom of a friend, as a momentary easement of our feelings. in this way, and in answers to addresses, you & I could indulge ourselves. we have probably done it, sometimes with warmth, often with prejudice, but always, as we believed, adhering to truth. I have not examined my letters of that day. I have no stomach to revive the memory of it’s feelings."^2

This is not unique to America or even to modernity. A broad reading of history shows that any human society, given enough time, will encounter periods when the stars align and there's a general degradation of civility, sometimes erupting in bloodshed, sometimes being remembered as a generally unpleasant time not to be spoken about.

The problems with American culture in particular being reduced to increasingly hostile and superficial tribal allegiances have antecedents dating back decades, well before AOL was even a thing.^4 The repeal of the Fairness Doctrine in 1985 enabled one-sided echo chambers to emerge via all extant communications media (notable in particular is the emergence of conservative talk radio like Rush Limbaugh).^5

"The empire, long divided, must unite; long united, must divide. Thus it has ever been."^6

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1 https://founders.archives.gov/documents/Jefferson/01-29-02-0...

2 https://founders.archives.gov/documents/Adams/99-02-02-6076

3 https://en.wikipedia.org/wiki/Alien_and_Sedition_Acts

4 http://txti.es/technorealism

5 https://en.wikipedia.org/wiki/FCC_fairness_doctrine

6 https://en.wikipedia.org/wiki/Romance_of_the_Three_Kingdoms