Calling it the "evil" option is incorrect, sure. I see three options for resolving the situation:
Free nightsong, kill nightsong, or bring nightsong back to Ketheric Thorm.
Sure, you will presumably see what this "heart of the Absolute" is if you bow and scrape enough, but disposing of a powerful enemy and giving Shadowheart a power-up in one fell swoop seems much more tempting. Thorm has made it clear that he wants to destroy the Astral prism, which makes him a dangerous foe to any character that wants to keep their free will. He's going to have to be disposed of sooner or later, even if you are just trying to take the Cult for yourself. Might as well take the shot when you have the chance.
