Look at the this from the boy’s eyes: he failed to pull the trigger on his captured foe, so now Dale is dead; and Dad failed to pull the trigger on his captured foe, so guess what happens next. As far back as Lost characters have tried to solve (without appealing to religion) the post-postmodern paradox of civilized men having to kill a dangerous prisoner, and while they struggle with the morality of it they beat their prisoner senseless to reveal how noble they are that they stop short of killing. But the paradox offered to viewers is a lazy trick, because it’s not a decision a single man makes; having a society around crowdsources the superego and allows it plausible deniability about tough moral questions, like targeted assassinations and bombing villages into oblivion: I didn’t do it, it was The Big Other, and I guess they know best what needs to be done. In real life Leader Rick would have found a way to be unable to stop Shane from killing the prisoner, and also why Rick was able to pretend that he couldn’t bring himself to euthanize poor Dale: he knew that the job would get done anyway. Sorry, Brother, this isn’t me doing this.
And yet still they do not call them zombies.