Steven Ozment on Calvin and Servetus

The following quote is taken from Steven Ozment's The Age
of Reform:1250-1550 (page 371):

In the controversy that followed the execution [of
Servetus], Castellio memorably summarized what to many
contemporaries became the simple truth of the episode.
'To kill a man,' he wrote, 'is not to defend a
doctrine, but simply to kill a man.' Although that
assessment has also proved to be history's view of the
matter, another century of religious warfare would be
required before this principle became firmly
established in law.