Arkat the Destroyer's illuminated followers infiltrate chaos cults like local Thanatar nests, learn their secrets, then use that information to help destroy the temple and kill the chaos worshippers.
How do Lightbringers and chaos fighting cults like Storm Bulls and Zorak Zoran react to this kind of skullduggery? Is there any possibility of at least limited tolerance for their activities? I mean, the Arkati are illuminates, they give power to chaos during the infiltration stage, but they help destroy chaos, providing information which might not be obtainable by other means, helping to gain access to hidden temples, improving the odds of success, helping to ensure none of the chaos scum survives the raid.
Without them, there would be more chaos.