What is more dangerous?
Someone who runs a loosely knit but still somewhat unified sectorwide organization, has lived for just about the entire time since the collapse, who is able to procure just about everything, can make your life miserable at a whim, yet who you may also bargain with and come to an understanding?
Or someone who, while not the head of an organization, has achieved legendary status due to the acts of terror committed, who inspires people to join this organization which has moles in every other organization, thus can get critical information whenever necessary, who may sometimes miss their goal, but if they achieve it, worlds may burn?
Honestly, a difficult question. While Kanta is more approachable and public, her goal is not destruction only. So that may count for something. Then again, if we can believe the conversations with Cotton, then he has also changed his known behaviour (at least towards the player). If we look at our first meeting with the Loke clone, and take what he says for truth (even if it makes little sense), it seems that Elissa, Gargoyle and Kanta are very much looking at the Galatia Academy's activities with interest and are regarding the relay hacking as a bit of a mischief.
About their sanity and the singing in general: are Cotton and the player, conventionally speaking, sane? For the latter I can accept that it depends on how you play. However for the former, while he hears the singing as well and it is of great importance to him, it does not diminish his former terrorist activities and religious fanaticism.
While you, the player, start hearing the singing when encountering the Ziggurat and later the gates, Cotton hears them first in prison, then later before you go meet him. Does he hear the same singing? I am not entirely sure.
In conclusion: I do wish the lore would flesh out lots of characters way more (especially Cotton). I'd read the hell out of every new tidbit.