I don't necessarily like it or agree with it, but I get it. Wars have secrets. Terrible things happen. Someone has to take the fall, but it's not usually the one in charge. There's politicking to it. As a show of good faith, after the war we see ONI trying to air out its dirty laundry. Truth gets out and someone has to be held responsible. They pin it on Halsey so that they can say "Look, some of us screwed up, but we're here to make amends. Justice will be served." Halsey's always been hated by ONI anyway (proven in, among other sources, her journal), so sacrificing her to the masses is hardly an issue. Think about it though: Halsey was the mastermind of the Spartan program. The augments, training, and selection process (which led to kidnapping children and leaving behind flash clones) was all her doing, her careful planning. She did it for the good of humanity, yes. But at what cost? It worked in the end, but hindsight is 20/20. If humanity had lost, if the Spartans had faltered, Halsey would only be remembered as another Mengele, assuming any bits of humanity survived. Some of her experimental augmentations had terrible effects, including death or severe crippling of the body (and some Spartans that "washed out" after augmentation undoubtedly weren't going to live the rest of their lives pleased with Halsey). Families were destroyed when they found the dead flash clones, thinking their precious babies had died. Some undoubtedly were suspicious, others shocked and suicidal, while still others may have divorced not being able to handle their loss. Across the board, many were affected in this way. To simply say that it was done "for the greater good" may not have been reason enough for the families who lost sons and daughters (or suicidal spouses). Coming clean becomes necessary. Halsey becomes the scapegoat as the mastermind. Was her part exaggerated? Sure, but that's how the universe works to cover more secrets. Can people really forgive crimes just because they ended up benefitting others? Certainly there would still be people crying for justice to be done. That's why a society wouldn't allow someone like Halsey to just walk. I'm sure we'll be seeing more of her going forward, but as it stands, I can appreciate how this could be a realistic interpretation.