Why did the church deal so cruelly with heretics? Why did most people of the Middle Ages answer this question differently?

The Church in the Middle Ages was interested in keeping people uneducated and illiterate. To do this, she made significant efforts. Such people are much easier to manage and collect material goods. Any dissent was considered heresy. Interpretation of church scriptures, which differed from the official one, is heresy. Scientific research in any field of knowledge is heresy. A person can write and read – almost always a heretic. In the Middle Ages, the church instilled in people its dogmas so much that the majority considered them the only correct ones and supported the Inquisition out of religious fear and their simple stupidity.