> Conversely the South African "truth and reconciliation commission" seems to have played a part in the healing of that country - but at the cost of leaving crimes unpunished.

You punish people to deter others for committing the same crime. The other benefit, revenge, has a scope that is too narrow to benefit the masses. So, if you are replacing an evil regime with a new regime and there is no possibility that the old regime will come back (apartheid has run by a small minority of the population) then there is no benefit from punishing past crimes. This is why the "truth and reconciliation commission" was so successful.

Very few countries can boast to such a peaceful political turnaround.