Why was heliocentric theory so controversial?

Answer 1

Since the ancient times of Greek philosophy the heavenly realm was divided from the earthly sphere. That the universe was centered around the earth, and often in particular some special earthly city seemed obvious, and enjoyed the backing of ecclesiastical authority by the time the heliocentric heresy rose to attack it.

In science, evidence trumps theory. Heliocentrism loosened the grasp of ecclesiastical authority in the domain of science, which was bound to generate substantial controversy at that time. Today the major scientific controversies occur as they conflict with political ideology.