For Finn to become the Mockingjay of Storm Troopers, he needs to regret shooting them. Instead not only he didn't feel any remorse but was enjoying himself. Therefore, I don't think that Trooper liberation is set up in TFA. We weren't supposed to be appalled that he shot them, but cheer with him. I don't think Troopers were meant to be sympathetic and humanized beyond Finn. He's one of a kind and that's really it.