Well, if we circle back to DB, we get to see a justification of "black magic" used to preserve life by Kumori, who is directly attached to Cowl, who is part of the Circle. That doesn't, in any way, rule out the Black Council being the in universe front for the the Outsiders. But it could indicate that members of the organization are capable of being turned. If Kumori were smacked in the face with proof that her noble goal of ending death would actually ruin existence, she might leave the Black Council or turn double agent. Combined with Nic's "One day" remark about being a Saint, I think it is entirely possible the end goals of the Black Council are EVIL, but they have deceived members with false hopes and impossible utopias.