There are major spoilers here for Halo 5: Guardians, ye be warned. In the Campaign, Cortana and the Warden Eternal believe that the Mantle of Responsibility has fallen, not to Humanity, but AIs. This has got to be some screwed up mentality, as even the Librarian’s AI called John Reclaimer and said Humanity is meant to inherit the Mantle. I wonder, why do you think Cortana and the Warden believe that the Mantle has now been bestowed upon AIs?