Efficacy of the Death Penalty
Thucydides 3.45.3-7 (speech of Diodotus on the fate of the Mytilenaeans; tr. C.F. Smith):
 All men are by nature
prone to err, both in private and in public life, and
there is no law which will prevent them; in fact,
mankind has run the whole gamut of penalties,
making them more and more severe, in the hope
that the transgressions of evil-doers might be abated.
It is probable that in ancient times the penalties
prescribed for the greatest offences were relatively
mild, but as transgressions still occurred, in course of
time the penalty was seldom less than death. But
even so there is still transgression.
 Either, then,
some terror more dreadful than death must be
discovered, or we must own that death at least is no
prevention. Nay, men are lured into hazardous
enterprises by the constraint of poverty, which
makes them bold, by the insolence and pride of
affluence, which makes them greedy, and by the
various passions engendered in the other conditions
of human life as these are severally mastered by
some mighty and irresistible impulse.
 Then, too, Hope and Desire are everywhere; Desire leads, Hope attends; Desire contrives the plan, Hope suggests the facility of fortune; the two passions are most baneful, and being unseen phantoms prevail over seen dangers.
 Besides these, fortune contributes in no less degree to urge men on; for she sometimes presents herself unexpectedly and thus tempts men to take risks even when their resources are inadequate, and states even more than men, inasmuch as the stake is the greatest of all — their own freedom or empire over others — and the individual, when supported by the whole people, unreasonably overestimates his own strength.
 In a word, it is impossible, and a mark of extreme simplicity, for anyone to imagine that when human nature is wholeheartedly bent on any undertaking it can be diverted from it by rigorous laws or by any other terror.