There is a tendency for all to judge the historical world through a 21st century lens and be shocked and revolted. The fact is that life was brief and brutal for all.
The fact is that capital punishment was a nearly universal punishment for all crimes. Heresy was treated as the most heinous of crimes by Protestant and Catholic alike. If one could be executed for taking ones purse or life, how much greater the punishment for the taking of ones soul.
Outside of the Catholic Church mercy was a rare commodity. The prevailing thought was that animals deserved deserved no mercy because they lacked a soul. Those who had willingly forfeited their soul had willingly assumed the status of animals. Fair and just by modern standards? No, but those weren't modern times or people.
Exactly. The TRUTH is that up until about three hundred years ago the Christian world had a legal system that is not unlike what Islam has today. By our standards it was truly barbaric, but it was also nothing more than a carryover from Mosaic law.