An excerpt from the Crisis article.
Pope St. John Paul II was well-known for his vigorous opposition to capital punishment. Yet in 2004, then-Cardinal Joseph Ratzinger—the pope’s own chief doctrinal officer, later to become Pope Benedict XVI—stated unambiguously that:
[I]f a Catholic were to be at odds with the Holy Father on the application of capital punishment … he would not for that reason be considered unworthy to present himself to receive Holy Communion. While the Church exhorts civil authorities … to exercise discretion and mercy in imposing punishment on criminals, it may still be permissible … to have recourse to capital punishment. There may be a legitimate diversity of opinion even among Catholics about … applying the death penalty … (Emphasis added)
How could it be “legitimate” for a Catholic to be “at odds with” the pope on such a matter? The answer is that the pope’s opposition to capital punishment was not a matter of binding doctrine, but merely an opinion which a Catholic must respectfully consider but not necessarily agree with. Cardinal Ratzinger could not possibly have said what he did otherwise. If it were mortally sinful for a Catholic to disagree with the pope about capital punishment, then he could not “present himself to receive Holy Communion.” If it were even venially sinful to disagree, then there could not be “a legitimate diversity of opinion even among Catholics.”
The fact is that it is the irreformable teaching of the Church that capital punishment can in principle be legitimate, not merely to ensure the physical safety of others when an offender poses an immediate danger (a case where even John Paul II was willing to allow for the death penalty), but even for purposes such as securing retributive justice and deterring serious crime. What is open to debate is merely whether recourse to the death penalty is in practice the best option given particular historical and cultural circumstances. That is a “prudential” matter about which popes have no special expertise.
We defend these claims in detail and at length in our book By Man Shall His Blood Be Shed: A Catholic Defense of the Death Penalty, forthcoming from Ignatius Press. What follows is a brief summary of some key points.
Sacred Scripture The Church holds that scripture is infallible, particularly when it teaches on matters of faith and morals. The First Vatican Council teaches that scripture must always be interpreted in the sense in which the Church has traditionally understood it, and in particular that it can never be interpreted in a sense contrary to the unanimous understanding of the Fathers of the Church.
Both the Old and New Testaments teach that capital punishment can be legitimate, and the Church has always interpreted them this way. For example, Genesis 9:6 famously states: “Whoever sheds the blood of man, by man shall his blood be shed; for God made man in his own image.” The Church has always understood this as a sanction of the death penalty. Even Christian Brugger, a prominent Catholic opponent of capital punishment, admits that attempts to reinterpret this passage are dubious and that the passage is a “problem” for views like his own.