We are facing a grave crisis of incivility.
"Civility: Civilized conduct, especially courtesy, politeness" (Thanks, Merriam-Webster.com)
Civility, in other words, is the ability to conduct ourselves as a civilization. To manage ourselves with courtesy towards one another, especially towards those with whom we disagree with. To be polite even when we fundamentally feel like the other person is wrong.
That has been tossed by the wayside in large part, it seems. People that we disagree with are no longer wrong, they are evil. They are not misinformed, they are willing believing and acting on the worst intentions.
In other words, they are no longer our fellow citizens. They are the enemy.
A society cannot long stand this sort of stress, of course. Incivility picks away at every bond that binds a culture together. It is the opposite of civilized of course, and given long enough, incivility gives way to uncivilized. People choose sides. And suddenly the side that started the incivility finds that the other side has adopted the same behavior and is acting just the same way. And the cycle increases in intensity and speed.
How long can such things last? I do not have a timer to tell this, of course. I do know that from the time of the first revolution of the Gracchi to the victory of Caesar it was approximately 85 years or so, and 19 years to go from the 1905 disturbances in Russia to the rise of Stalin and that it only took 14 for Germany to go from defeat in WWI to Hitler taking power in 1932. So things tend accelerate.
The difficulty with civilization, of course, is that everyone misses it after it is gone - especially those who enjoyed its benefits as they tore at its vitals. For the natural, uncivilized world is a very deadly and dangerous place indeed.