In our own times the Church has not modified this ancient and venerable teaching. Pope St. Pius X promulgated a catechism which also, following Trent’s arrangement, refers to capital punishment in discussing the Fifth Commandment:
Q. Are there cases in which it is lawful to kill?
A. It is lawful to kill when fighting in a just war; when carrying out by order of the Supreme Authority a sentence of death in punishment of a crime; and finally, in cases of necessary and lawful defense of one’s own life against an unjust aggressor. Papal teaching was in accord with this view as late as the pontificate of Pope Pius XII, who stated in an address that “when it is a question of the execution of a man condemned to death it is then reserved to the public power to deprive the condemned of the benefit of life, in expiation of his fault, when already, by his fault, he has dispossessed himself of the right to live.”
So it is not surprising that even up to the very eve of the Second Vatican Council, Adolph Tanquerey could address the issue of the death penalty in his seminal moral theology text by first stating this principle:
“The civil authority is able to punish with the ultimate punishment of death evildoers duly convicted of the most grave crimes, as often as the public good requires (quoties id requirit bonum publicum).” (emphasis added).
Code:
Father Tanquerey supports this principle by demonstrating that recourse to capital punishment is strongly rooted in both history and human psychology, and ends his discussion by emphasizing the ethical probity of the death penalty:
Justice demands that the offended moral order be repaired and restored by a congruent satisfaction; and therefore the duty devolves upon the leaders of the Republic to take care that grave crimes are punished by proportionate penalties; for otherwise the moral order is disturbed and endangered. Certainly there are crimes of such gravity committed which, in the general estimation, will only be able to be expiated by means of the death penalty; of such a kind especially is murder cruelly committed after mature deliberation; for crimes which are the greatest affront to the moral order, and encompass the greatest harm, require of their nature the greatest punishment, that is, capital punishment. And therefore this rule is established by common sense: ‘Whoso sheds the blood of man, shall by man have his blood shed.’
Sacred Tradition, then, has consistently viewed capital punishment as a vindication of the sacredness of life. This is clearly shown by the way various Doctors, Popes, and Councils have firmly rooted their validation of the death penalty in discussing the Fifth Commandment; not only to explain why capital punishment does not offend against this Commandment, but also to underscore that by this punishment the sacred gift of life is vindicated. Clearly, the moral approval of capital punishment in the sources just examined is based, not on political expediency or practical concerns such as deterrence, but on obedience to the Fifth Commandment and in recognition of the sanctity of life.
Moreover, as a perennial teaching touching on a matter of morals, it is impossible to avoid the conclusion that the Church’s teaching on the death penalty belongs to the Ordinary Magisterium of the Church. It is a teaching to which the following statement of the Fathers of Vatican I applies:
T]he Church would lose its immutability and dignity and it would cease being a life-giving society and a necessary means of salvation if it could wander from the safe path of truth in matters of faith and morals, and if, in preaching and explaining these matters, it could deceive or be deceived.
The moral liceity of the death penalty thus belongs to the perennial moral teaching of the Church, and one would have to posit that the Church had erred and thus failed in its Divine mission, if one would affirm that the death penalty is in fact always and everywhere immoral. The Church would, for its entire history, have not taught the truth to society about morality, but rather affirmed the moral good of what is in fact a moral evil. But this is impossible for a Catholic to admit. The Church could no more have taught erroneously that capital punishment is not only licit but laudable than She could have erroneously taught that use of artificial contraception is always and everywhere contrary to the moral law. The Church is Divinely protected from leading men astray in its constant teachings concerning moral issues. She is the teacher and informer of consciences and would have failed in Her mission if She had suddenly been found to have erred for so long on such a fundamental issue of morality.