This is an interesting discussion. Personally, I think Pope John Paul II’s position has to be developed more. It almost seems to boil down to, “You can’t execute anyone, unless you don’t have the proper facilities.”
Avery Cardinal Dulles wrote an interesting article on the Death Penalty where he gives a brief overview of the development of the opposition to it:
"The mounting opposition to the death penalty in Europe since the Enlightenment has gone hand in hand with a decline of faith in eternal life. In the nineteenth century the most consistent supporters of capital punishment were the Christian churches, and its most consistent opponents were groups hostile to the churches. When death came to be understood as the ultimate evil rather than as a stage on the way to eternal life, utilitarian philosophers such as Jeremy Bentham found it easy to dismiss capital punishment as “useless annihilation.”
Many governments in Europe and elsewhere have eliminated the death penalty in the twentieth century, often against the protests of religious believers. While this change may be viewed as moral progress, it is probably due, in part, to the evaporation of the sense of sin, guilt, and retributive justice, all of which are essential to biblical religion and Catholic faith. The abolition of the death penalty in formerly Christian countries may owe more to secular humanism than to deeper penetration into the gospel.
Arguments from the progress of ethical consciousness have been used to promote a number of alleged human rights that the Catholic Church consistently rejects in the name of Scripture and tradition. The magisterium appeals to these authorities as grounds for repudiating divorce, abortion, homosexual relations, and the ordination of women to the priesthood. If the Church feels herself bound by Scripture and tradition in these other areas, it seems inconsistent for Catholics to proclaim a “moral revolution” on the issue of capital punishment."
leaderu.com/ftissues/ft0104/articles/dulles.html