Society creates law to apply society's own accepted level of justice, built up and evolved over centuries. The purpose is to provide an accepted framework for behaviour that benefits the majority.
This is exactly how it should be in the case of Venables and Thompson: to decide the benefits to society. Laws have changed but the principles are the same. If we apply this straightforward approach, without any notion of revenge as mooted by those who would cloud the issue, then our first requirement is to decide society's needs.
Society needs contributors. It is the empirical basis of how we function. Because of the dreadful acts of violence by Venables and Thompson we have been for ever deprived of the contribution of Jamie Bulger, an unknowable quantity. However, as to their own future contribution, we can and must make certain judgmental assumptions.
First and foremost, the potential for negative effects - given their crime and how it is so far removed from normal acceptable behaviour, with so little indication of its likelihood - must be seen to be massive. Furthermore, there would be a serious emotional effect on a significant section of the community, the Bulger family being the most obvious. Secondly, to counterbalance the equation is the possible benefits to society. It has to be said that the overall effect of their input, as a percentage of the population, could only be tiny, and it is this fact, in the light of the grotesque nature of their crime, that should count against them. The final consideration, that of benefit to the boys themselves, should never be taken into account, as in this case it could never be part of justice, given that there can never be any benefit to Jamie Bulger.