A key to why the Stygian Heresy is so threatening to mainstream Malkioni can be found in Arkat’s apocryphal retort to the missive of King Nralar demanding that the Hero end sacrifice to the Gods of Darkness:
“The Great Mystery is not subject to rational understanding. It can only be experienced. Only those who have experienced the mystery can meaningfully speak of it; only those who have been a god can meaningfully understand the dangers of divinity. The Great Mystery cannot be dissected or reduced, it simply is. I have experienced it, I have been a god, I have been Death, I have been a krjalki (monster), and so I shall continue to do what I have pledged to do.”
See also
“To destroy a monster, I became a monster. To wield Death, I became Death.”
This sort of talk disturbed our poor rationalists to the very marrow of their bones!
Of course, Arkat’s followers went into hiding during the long centuries of Seshnegi oppression. When they re-emerged at the end of the Second Age they were barely recognizable.
After the destruction of the Dark Empire, various groups seeking to preserve Arkat’s teachings scattered. Some established strongholds in Ralios, others organised in secret opposition to the God Learners. When the Middle Sea Empire conquered and annexed lowland Ralios circa 900, these secret groups proliferated, many claiming to follow a Hidden Archon, or concealed disciple of Arkat. These groups fought with each other as fiercely as they fought the God Learners (and later the Rokari).
After the destruction of the Middle Sea Empire and Seshnela, these sects came out in the open. Some seized control of a city, only to lose power to a rival. Common threads include:
A group claims to be in contact with the Hidden Arkat (or at least with the hidden heir of Paslac)
A group claims to know when Arkat will return and is preparing for his return.
A group claims to know THE secret of Arkat, the one he whispered to his truest companion (whose biological or spiritual descendant founded the sect) and survived the God Learners.
From the perspective of any given sect, all of the other sects are either liars, fools, or worse.
For a Real World point of comparison, the plethora of Ism’ali sub-sects in the 8-13th centuries is a good starting point – Qarmatians, Nizari, Druze, Darazites, Alawites, Adawiyyites, and so on.