Much of the tendency of the “Marietta’s True Crime” debate was to put Marietta and Hermione on a moral see-saw. The unspoken premise was, the more justified (or sympathetic) Marietta was in approaching Umbridge and telling her about a certain illegal student organization, the less so was Hermione for “punishing” Marietta by mutilating her, perhaps for life.
(Only “perhaps,” fine. Just as it’s only “perhaps” that Dolores scarred Harry permanently with that Blood Quill. We know from Mad-Eye, Albus, Arthur, Bill, Draco, and Harry himself that magical injuries can leave lifelong scars. But still, it’s not explicitly stated in canon that Harry, fantastically old, died with that scar still on his hand. For anything we know, it vanished one page after its last mention in DH. So no one can accuse Umbridge of scarring Harry for life, right? But in canon, the last we saw, Harry bore “I must not tell lies” engraved into his flesh. In canon, the last we saw of Marietta, she was trying desperately to hide the word “Sneak” blazoned across her face.)
Now, in schoolkid morality, tattling on someone to the teacher is a crime. Tattling on a friend, after explicitly promising not to tell, is the worst crime possibly imaginable!
We, however, are adults, and have larger imaginations.
And Hermione’s betrayal of her schoolfellows (and Hermione’s other crimes) may be judged without reference to Marietta’s transgression.
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