Allecto was a Roman fury. When Juno said "If I cannot change the will of Heaven, I will release Hell" (in Virgil's Aeneid) she was talking about turning Allecto loose on the world. Allecto's hair is all beautiful dark snakes, which she shoots into the hearts of mortals to drive them insane. She is described as having 'a thousand types of mischief'. She's basically quite a heinous lady. When she returns to the underworld, the world is 'relieved of her presence'. How can you NOT love someone like that?