Not dishonest, but certainly mistaken

The heretics were never dishonest men; they were mistaken men. They should not be thought of as men who were deliberately setting out to go wrong and to teach something that is wrong; they have been some of the most sincere men that the Church has ever known. What was the matter with them? Their trouble was this: they evolved a theory and they were rather pleased with it; then they went back with this theory to the Bible, and they seemed to find it everywhere.”

― Martyn Lloyd-Jones, Studies in the Sermon on the Mount