Why doesn't the Catholic Church kill heretics anymore? So the Catholic church used their influence to sanction the execution of so-called "heretics" and now they do not. Somewhere in the middle they stopped supporting executions based on heresy.

Why did they stop? Was a formal reason given? This question sheds some great light as to when they stopped and began hinting as to why but doesn't really dig deep into it.



Important Note: The premise of my question is that the Catholic church had the de facto ability to convict and order executions based on so-called "heresy" and that it followed through with that ability. I acknowledge that technically the Catholic church itself never executed anyone, but through its influence on secular government had, in effect, the ability to execute through excommunication.

Some examples of this include The Massacre of Mérindol, Jan Hus, Cathar Crusade, Inquisitions, Joan of Arc, Priscillian, and the Stratford Massacre.
To the question, "When did the Church stop executing people" I answer that is a false premise. Probably akin to "when did you stop beating your wife?"

To the question, "Can a reasonable differentiation be made between the actions of the state acting in the name of religion and the policies of the religion proper?" I suggest that you look into emperor Otto and how (despite his apparent contrition, immediately drove the Pope into exile as soon as his excommunication was lifted). Or, perhaps more on topic, you could look at the consistent efforts of the Papacy to stem the violence brought by the Spanish Crown during the Spanish Inquisition. Several examples:


Near the outset of the Inquisition, in a letter of April 14, 1482, Pope Sixtus IV instructed the Spanish to ensure due process, allow legal counsel and appeal to Rome.[53] King Ferdinand defiantly rejected Papal control, the Inquisition becoming thereafter a tool of the monarchy, rather than the church.
The Pope tried to allow for appeals, but the crown only allowed that by royal approval
Torquemada actually systematized what could only be considered mob rule.
And finally an appropriate quote, "In 1498 the pope was still trying to...gain acceptance for his own attitude towards the New Christians, which was generally more moderate than that of the Inquisition and the local rulers."


To the question, "When did the policy of Church enacted executions end?" This requires proof that the Church had a policy of executing criminals, as an entity independent of the state. The evidence to this is very lacking.

To the question, "When did the policy of Church-sanctioned executions end?" The answer is that it never has: given appropriate circumstances (rare in first-world countries), the Church does make allowance for the death penalty.

To the question, "When did the policy of Church-sanctioned execution of religious or political dissidents end?" Again, the answer is that it didn't. Believe it or not, the Church is not in the business of dictating punishments for crimes. I don't know of any document which has ever said that the state does not have the right to execute criminals. 

I would imagine that a significant number of churchmen, and indeed a vast majority of the populous, prior to the mid-twentieth century would have allowed for executing someone who has committed treason. I would also imagine that preaching dissidence in Medieval Europe would have been viewed as treason. (This is not a real stretch, I can think of one case where speaking out against the state was punishable by torture and death in sixteenth century Holland.)

To the question, "When did the Church stop having the policy of rendering correct judgements on matters heretical?" Again, the answer is never. 

To the question, "Should the Church, knowing the intentions of the state, render a correct verdict?" And I think that answer is very loaded and beyond the scope of your question.



On an interesting side note: it should be stated that the purpose of the inquisition, was not to kill heretics, but to save souls. Thomas Madden states the position:


  [t]he Inquisition was not born out of desire to crush diversity or oppress people; it was rather an attempt to stop unjust executions... The simple fact is that the medieval Inquisition saved uncounted thousands of innocent (and even not-so-innocent) people who would otherwise have been roasted by secular lords or mob rule.


The article goes on to reinforce this idea by pointing out:


  Madden argues that while medieval secular leaders were trying to safeguard their kingdoms, the Church was trying to save souls. The Inquisition provided a means for heretics to escape death and return to the community.


This is remarkably far from the implicit accusations in the question. I'd dare say, this was the opposite.