He didnt even stab the guy at the end, instead he shot him, changing that changes the whole tone of the piece, stabbing someone is a way more visceral and (I have read) personal and difficult method of murdering someone, shooting the mutant removed this, and a big part of the story arc is the change in the family, (and Doug in particular), changing ( mutating, if you will🙂)and becoming savages themselves, so I feel this undermined the impact of the moral commentary.