The heresy of Arianism arose when a pastor from Libya named Arius (250–336) opposed the Orthodox idea that Jesus is co-eternal with the Father. In my article 'The Tenacity of Saint Athanasius,' I suggest that this heresy was attractive because it made the Christian message more politically correct.
Like modern day Jehovah’s Witnesses, Arius argued that if Jesus was God’ son, then by definition he must have had a beginning to his existence and could not also be eternal God. Arius gathered a following of other pastors who walked around chanting, “There was a time when he was not, there was a time when he was not,” indicating their belief that Jesus was a creature with a beginning rather than the eternal Son of God.
The reason this heresy was appealing is because for hundreds of years Mediterranean culture had revolved around the worship of the emperor and various other demigods. If Jesus was simply a great man or angel, then serving Him was compatible with the worship of these other deities. Arianism was thus found to be highly attractive to those in positions of power.