http://www.chickenjoke.com/

Plato: For the greater good.

Aristotle: To fulfill its nature on the other side.

Karl Marx: It was a historical inevitability.

Machiavelli: So that its subjects will view it with admiration, as a chicken which has the daring and courage to boldly cross the road, but also with fear, for whom among them has the strength to contend with such a paragon of avian virtue? In such a manner is the princely chicken's dominion maintained.

Hippocrates: Because of an excess of light pink gooey stuff in its pancreas.