When you consider the theological approaches the Church has taken with regards to the death penalty (and not just issues of circumstance), it is not necessarily the case that the Church was gung-ho about it, even early on, but it did see it as, under very specific circumstances, a legitimate tool of the state that can be used for the common good. This is why you see in the Catechism of Trent,
“Another kind of lawful slaying belongs to the civil authorities, to whom is entrusted power of life and death, by the legal and judicious exercise of which they punish the guilty and protect the innocent. The just use of this power, far from involving the crime of murder, is an act of paramount obedience to this Commandment which prohibits murder. The end of the Commandment is the preservation and security of human life. Now the punishments inflicted by the civil authority, which is the legitimate avenger of crime, naturally tend to this end, since they give security to life by repressing outrage and violence. Hence these words of David: In the morning I put to death all the wicked of the land, that I might cut off all the workers of iniquity from the city of the Lord.”
However, the early Church was also queasy about DP, but whenever it appealed against its use, it never did so on the grounds of human dignity, but rather on the grounds of mercy. The DP done right is just, but for the sake of one’s soul, mercy becomes a factor as well in the Christian state. To make DP, even under the strict circumstances, a violation of justice and not just a lack of mercy, would contradict the teachings of the Church, and not simply be a development of its teaching.
The main contention here is not even between people who are gung-ho about DP and those who call it a human rights violation. It is between people who adhere even to JPII’s formulation, and vs some of the approaches that Francis and those after him are taking in transforming DP into an intrinsic evil.