It must be just, because it has been taught by St. Thomas Aquinas, St. Augustine, The Council of Trent, and many popes, including Pius XII, Innocent I, and Innocent III. Not to mention Genesis 9:6
Whether it is the most just and appropriate punishment is another question. However, since the above taught capital punishment, it is likely that it is the best punishment. I have never heard one of them make “life imprisonment without payrole” a possible punishment for murderers.
The case of the woman cannot be used as a reason to end the death penalty; if it were linked with capital punishment, then the Church would never have allowed it through all these centuries.
The “eye for eye” does not mean that public officials vested with authority from God are not allowed and obliged to punish the guilty. When Christ talked about forgiveness, he was talking about forgiving enemies; he was not, however, dumping the need for punishment and retribution. Again, if that were the case, the Church wouldn’t excommunicate people because that would be “unmerciful.”
It must be remembered that just punishment is in reality an act of mercy. It is for the criminal’s own good that he is punished, so that he can try to make up for what he did and thus make himself worthy before God. The so-called “love” that never condemns and never punishes wrongs committed is not true love, since, by withholding just punishment, one is not so concerned of the punishment the person may have to endure in the next life as a result of his actions being unchecked.
Justice is the primary purpose of punishment; safeguarding society is secondary. Thus, even if prisoners are 100% unable to do any harm, it does not change the fact that they must make full retribution for their crime(s). As far as repenting, the greatest chance for repentence comes when a man knows that he will be put to death and meet his Maker within a short period. This may fill him with a fear of hell, and thus a remorse for his sins.
The contradiction I see is that he first talks about justice being the primary purpose of punishment, and then says the death penalty should only be used when it would be necessary for safeguarding society, a secondary purpose. Thus he makes a secondary purpose the primary purpose.
The only way I see that there is no contradiction is if JPII believes that the death penalty is not necessarily the most just punishment for murder. But then another question arises: what, then, could substitute for the death penalty and make equal retribution? I don’t see anything else being equal.