Totally agree, but the divergence of my take on the book’s ending versus the movie’s interpretation began well before the consumption of the berries.
I watch as he painfully makes it to his feet. Then he’s moving toward me, as if in slow motion, his hand is pulling the knife from his belt—
Before I am even aware of my actions, my bow is loaded with the arrow pointed straight at his heart. Peeta raises his eyebrows and I see the knife has already left his hand on its way to the lake where it splashes in the water. I drop my weapons and take a step back, my face burning in what can only be shame.
“You’re not leaving me here alone,” I say. Because if he dies, I’ll never go home, not really. I’ll spend the rest of my life in this arena trying to think my way out.
Because the entirety of the scene in the books is, to me, a good portion of the reason why the districts are inspired to rebel. Katniss’ experiences in the arena parallel that of Panem: she has spent the entirety of her time focused on survival and has learned that even the barest of graces extended by the Capitol-that twenty two children may die instead of twenty three-will eventually prove illusory. There is so much emotional power in that first excerpt, when Katniss is still in survival mode and immediately prepares to shoot Peeta. Once she sees that he means only to disarm and sacrifice himself, she realizes that not only was she played by the Capitol again but that to continue to comply with their rules would mean the irrevocable loss of her humanity and her sanity.
There is an emotional desperation to the end of the book, from this realization right through to her breakdown during Peeta’s surgery, that is lacking in the movie. Katniss was pushed to the very brink of what she could endure, and yet she still resisted the government’s cruelty. Katniss often accuses herself of being selfish, but she has rejected time and time again the every-person-for-him-or-herself mentality that seems to be necessary for survival in Panem, from volunteering for Prim to her alliances with Rue and Peeta. If Katniss were playing according to the Capitol’s rules, she has absolutely nothing to gain from this suicide pact because she has essentially been guaranteed victory by the combination of Peeta’s willingness to sacrifice himself and the severity of his injuries which have left him on the point of death. Katniss could not only survive, but win, and no one in Panem would fault her for her actions; no one, that is, except herself. The ending is Katniss choosing to think beyond mere survival, and Panem was then able to realize that it could (and should) be able to do the same.