Still, even if we take the whole story into account, if killing the one immune person before doing all kinds of tests on her, making a solid plan to get the cure created, stored and distributed, etc, really was a terrible idea worth stopping — was really killing so many of the world's few remaining humans, including a desperately needed doctor, the way to go about it? If the Fireflies are half-assed, isn't Joel too? Take some hostages and negotiate, maybe?