We hear a lot--and are starting to see more of--the dangers of overheated political polarization. Here's a quote from Thucydides' Peloponnesian War about how Greek democracies and city states went off the rails in his day:
"Words had to change their ordinary meaning and to take that which was now given them. Reckless audacity came to be considered the courage of a loyal ally; prudent hesitation, specious cowardice; moderation was held to be a cloak for unmanliness; ability to see all sides of a question, inaptness to act on any.Frantic violence became the attribute of manliness; cautious plotting, a justifiable means of self-defence. The advocate of extreme measures was always trustworthy; his opponent a man to be suspected...
The fair proposals of an adversary were met with jealous precautions by the stronger of the two, and not with a generous confidence. Revenge also was held of more account than self-preservation. Oaths of reconciliation, being only proffered on either side to meet an immediate difficulty, only held good so long as no other weapon was at hand; but when opportunity offered, he who first ventured to seize it and to take his enemy off his guard, thought this perfidious vengeance sweeter than an open one, since, considerations of safety apart, success by treachery won him the palm of superior intelligence."