Please note that the story does not portray a prisoner's dilemma. The frog has absolutely nothing to gain by carrying the scorpion across, and is therefore a foolish altruist, proving the truth of the adage, "No good deed goes unpunished." But it is not hard to turn the story into a prisoner's dilemma, as follows.
The frog desires to cross the stream but is afraid of a stork on the other side. The scorpion has no means to cross the stream but is capable of scaring the stork. If the frog carries the scorpion across, the scorpion will reciprocate by frightening away the stork; the scorpion will have crossed the stream and the frog will be safe. The apparent sucker's payoff for the frog is that the scorpion will slip away without scaring the stork once the frog has gone to all the trouble of carrying him across. There is no apparent sucker's payoff for the scorpion--the frog's major opportunity for defection is not to carry the scorpion, but, since the scorpion will not yet have had the opportunity to extend its cooperation it will not have lost anything (the moves are not simultaneous). Perhaps the frog's defection may consist of eating the scorpion, once it has scared off the stork.
In any event, the scorpion's unexpected and selfdestructive defection raises the issue of how to counter a player who defects first, and defects in a way that prevents you from retaliating on the next move (your life has ended in the meantime.) All assassins and terrorists play the game this way. Because they are willing to die--it is their nature--the future has no shadow for them. This madness is not unique to humans--the bee that stings to defend the hive, then dies, is a suicidal defector in nature.
Gandhi succeeded in his variation on the prisoner's dilemma because the British were not willing to resort to the ultimate defection. A player, like the Nazis, willing to stop at nothing, creates an illogical loop much like the one that results when two players play a series for a known number of moves. Since, on the last move, the future has no shadow, I might as well defect. Since the other player will certainly be smart enough to defect on that move as well, I may as well defect on the move before, when he may still be cooperating. But, since he is smart enough to reason this through the way I did, he will probably defect on that move too. So again I will consider defecting a move earlier. But so will he. The result: we both defect on the first move and each move afterwards.
Because the scorpion will kill you as soon as it is given a chance, you must find a way to defect earlier than the scorpion, and decisively. But the scorpion will study the situation, looking for a way to defect earlier than you can; so you must assume he will do so, and seek to defect earlier still. Like gunfighters in a Western movie who run down the street at each other, howling and shooting as soon as they catch sight of each other, the prisoner's dilemma escalates into an immediate duel to the death. The concept of a pre-emptive strike expresses nothing other than a strategy based on defecting early and decisively. Tarquinian's symbolic cutting of the tops from the tallest flowers, or the massacre of opponents after any coup d'etat in history, are other examples.
It is the scorpion that pulls humanity down. If you are not yourself a scorpion, you still are unable to play every move of every game in the cooperation zone, because sooner or later you will meet a scorpion. Not every scorpion is a suicide bomber; the law partner who made a successful motion to cut my draw, forcing my resignation from a law firm, suffered the symbolic fate of the scorpion when the firm's biggest client (the one I alone knew how to service) left as a result, and the firm folded. Yeats' judgment that "things fall apart, the center cannot hold", because "the worst are full of passionate intensity" is a recognition of the fact that there are scorpions.
Scorpions may know the consequences, and not care, like the suicide bomber, or may, through vanity and denial, refuse to see the consequences, like my ex-partner. In any event, the effect is the same: a player defects when there is no reason to, and something--a life, an enterprise--ends as a result.
Game theory does not really take scorpions into account. It holds that people will defect because that is in their best interest--because the future has no shadow. Game theory fails as a tool when we are dealing with sociopathology or extreme denial. The human dilemma is that all progress ultimately fails or at least slides back, that anything once proven must be proven again a myriad of times, that there is nothing so well established that a fundamentalist (of any religion or stripe) cannot be found to deny it, and suffer the consequences, and then deny that he suffered the consequences.
All rivers begin in the human heart and, as I said recently in my Auschwitz essay, the human heart is infirm. The saddest saying I ever heard, "trees never grow into heaven", will be true for so long as we have scorpions.