For centuries, the Catholic Church enacted capital punishment on a large scale. But in modern politics, the Catholic Church has been a staunch supporter of life. When did this change?
Technically speaking - Catholic Church never enacted the death penalty - the legal fiction they used was "handing the condemned over to the secular authority". They themselves merely presented the evidence which the laity used to condemn the accused. When they went from "supposedly" being against the state killing to doing so in reality is a different question. I'm merely clarifying your assertion that the Church "enacted capital punishment on a large scale". It technically never did, not even once.