As chancellor it was his [Thomas More’s] duty to enforce the laws against heretics […] As he himself wrote in his “Apologia” (cap. 49) it was the vices of heretics that he hated, not their persons; and he never proceeded to extremities until he had made every effort to get those brought before him to recant. How successful he was in this is clear from the fact that only four persons suffered the supreme penalty for heresy during his whole term of office.

(From the Catholic Encyclopaedia)

Or in other words, he only killed four people for disagreeing with him.