Calvin gets a lot of stick for approving of the death of Michael Servetus.
But, as usual, these things are not straight forward. Calvin lived in a different era, and even within that period, his compassion shines in the darkness.
Derek Thomas, in John Calvin: A Heart for Devotion, Doctrine, Doxology, offers an alternative perspective on the "Cruel Calvin Caricature. . .
To some, including John Knox of Scotland, the city (Calvin's Geneva)* was the closest thing to heaven they had seen. For others, such as Michael Servetus, whose execution in 1553 (and Calvin's approval of it) is re-told with untiring frequency, found Geneva stifling. But Servetus was found guilty of heresy (anti-Trinitarianism) and of being a disturber of the peace (he had been warned not to enter Geneva), and would have fared equally badly in a Catholic city had he been caught in one. His execution is not an example of intolerant Calvinism, but of a layer of sixteenth-century civil jurisprudence in central Europe, where various lifestyles were considered untenable and punishable by law in a way that humanist societies of our own day would react to with apoplexy. He had been found guilty by a civil court of twenty-five men, and Calvin himself spent hours with Servetus, urging him to repent in order to avoid the inevitable sentence. Calvin's request for a less-painful execution (Servetus was burned) was refused. Arguably gentler Reformers, including Martin Bucer and Philip Melanchthon, fully approved of his death.
*Parenthesis added by blogger for clarity