Reciprocity (n.) seems only fair, good for good and evil for evil, and it is exactly what every community on the planet has always done, with familiar results.
Reciprocity (n.) wins precisely because each rival denies it: all chase difference with the same strategies at the same moment, and the denied reciprocity haunts them.
Reciprocity (n.) gone bad feeds on itself and needs no external cause to continue; once the outside cause fades, the first scapegoat ends the crisis.
Reciprocity (n.) turned evil gets worse by its own logic: half of the combatants think justice is done because they are avenged, and the other half strike back to avenge themselves.
Reciprocity (n.) is only ever perfect at the extremes — total violence or total nonviolence — and humanity has managed only the first.
Reciprocity (n.) terrified archaic peoples for good reason: whenever it broke through the screen of custom, it became runaway competition and then mutual violence.