A short quote from Wikipedia on Servetus:
"As Servetus was not a citizen of Geneva, and legally could at worst be banished,
the government, in an attempt to find some plausible excuse to disregard this legal reality, had consulted other Swiss Reformed cantons (Zürich, Bern, Basel, Schaffhausen). They universally favored his condemnation and suppression of his doctrine, but without saying how that should be accomplished.[33]
Martin Luther had condemned his writing in strong terms.[34] Servetus and Philip Melanchthon had strongly hostile views of each other.
The party called the "Libertines", who were generally opposed to anything and everything John Calvin supported, were in this case strongly in favor of the execution of Servetus at the stake (while Calvin urged that he be beheaded instead). In fact, the council that condemned Servetus was presided over by Ami Perrin (a Libertine) who ultimately on 24 October sentenced Servetus to death by burning for denying the Trinity and infant baptism.[35] Calvin asked that he be beheaded instead of burnt, knowing that burning at the stake was the only legal recourse.[36] This plea was refused and on 27 October, Servetus was burnt alive—atop a pyre of his own books—at the Plateau of Champel at the edge of Geneva."
Even those strongly opposed to Calvin were in favor of the execution. I only wish the Councils of Geneva had shipped him back to Vienne where he escaped prison. However, it would have sent a message to other heretics to those who cared not for the souls of men desiring to follow in the footsteps of Servetus. Somewhere I read that (at least) one such person was detoured from following in the footsteps of Servetus after the execution of Servetus.
It cannot be emphasized enough that the sentence was pronounced by the Councils of Geneva, not Calvin. If Calvin had the authority, Servetus would have been beheaded, rather than burned. That in itself shows where Calvin stood with the Councils.
As for sic implications that John Calvin (while not even a citizen), took some twisted delight in the burning of Servetus when it could not be further from the truth, Tim Challies states truthfully on his blog:
"It should be noted that Calvin was the only person who suggested a lighter sentence, asking the court to allow Servetus to die painlessly by beheading. Calvin prayed with and for Servetus and earlier in his life had sent Servetus a copy of his
Institutes. Interestingly, Servetus returned the book with many abusive and insulting comments written in the margins. Despite this offense, Calvin showed clear pastoral concern for this man’s soul."
tim challies blog
John Calvin only had a part in Servetus' arrest and investigation, as in recommending to Genevian authorities to investigate him. He was sorry that Servetus went against his advice to come to Geneva, and sorry the council did not give him a quicker less painful death. Not only is there no evidence of John Calvin being unrepentant, it is a judgmental attitude considering he:
"preached over two thousand sermons. He preached twice on Sunday and almost every weekday. His sermons lasted more than an hour and he did not use notes." (not to mention tens of thousands of pages of commentary on Scripture, the first Protestant systematic theology, among his many other writings)
"Within Geneva, Calvin's main concern was the creation of a
collège, an institute for the education of children. Although the school was a single institution, it was divided into two parts: a grammar school called the
collège and an advanced school called the
académie. Within five years there were 1,200 students in the grammar school and 300 in the advanced school. The collège eventually became the Collège Calvin, one of the college preparatory schools of Geneva, while the académie became the University of Geneva."
"when he could not walk the couple of hundred yards to church, he was carried in a chair to preach. When the doctor forbade him to go out in the winter air to the lecture room, he crowded the audience into his bedroom and gave lectures there. To those who would urge him to rest, he asked, “What? Would you have the Lord find me idle when he comes?”
None of these historical facts bear the mark of a bitter unrepentant sinner.
It is difficult today to even wrap the mind around what it would have been like to live in Europe during the Reformation times. Blood was shed on every side in the region, consider the Puritan John Foxe and his "Book of Martyrs", with descriptions of executions of Protestants under "bloody" Mary I. Catholics and Protestant persecuted the Anabaptists. It was a dark time in Christian history, let's be careful not to put out the few Protestant lights that burned especially bright in a time of great darkness.