In the bad old days, things could be pretty tough. In the Middle Ages people who committed treason were drawn and quartered, which was definitely not a pleasant way to go. (Check out the link.)
Now we're ever so much nicer to criminals. But why? Is it because we've learned that it's good to be kind?
The following argument says that's not the case, although we might like to believe otherwise: In the Middle Ages, the kinds of detective techniques used to solve crimes and punish the guilty didn't exist. There was therefore a much smaller chance of getting caught. In order to prevent chaos, the only solution was to make the price paid by those who were caught very steep.
Perhaps one day there will be a way to calculate the overall amount of punishment meted out to criminals based on the following formula: Multiply the probability of getting caught times the amount of suffering that is incurred by those who are.
Hypothesis: if/when there is ever some reasonable way of assigning numbers to those two factors for various societies that have proven to be stable, the product will be (roughly) a constant.