There was no crime greater in the middle ages than to be accused of heresy. People would rather be accused of murder. Why? Murder was a violation of a social law. You were punished and could potentially re-enter society after it. Murder also came with a bunch of evidentiary requirements.
Heresy, on the other hand, did not. Anyone could be accused of heresy over just about anything and would find it very difficult to prove otherwise.
Heresy was a renunciation of the entire order of the accepted universe. It brought with it ex-communication from your community, your church/faith, your afterlife, and almost exclusively your present life.
Once accused of the big H it was never a question of getting out of it, innocent people regularly confessed to heresy and died for it simply to preserve their eternal soul. And this very much suited the authorities of the day because rituals of public punishment/atonement reinforced social order and reasserted primacy of the entire way of being.
Taken from The Great Courses’ Explaining Social Deviance Lecture 2: Demonism