Why punishment is worth it in the end

Is punishment a destructive force that breaks societies or part of the very glue that holds them together? Last year, I blogged about twostudies that tried to answer this question using similar psychological games. In both, volunteers played with tokens that were eventually exchanged for money. They had the option to either cooperate with each other so that the group as a whole reaped the greatest benefits, or cheat and freeload off the efforts of their peers.