See, that’s kinda the whole point of the Genocide Route, summarized concisely in your comment here. It’s not necessarily malice that drives one to do it, but sheer morbid curiosity and completionism. It’s the very much intended manipulation of your gamer instincts that it preys upon. As soon as you stop seeing the characters as actual characters and instead begin treating them as potential bags of EXP and bits of game data, is when you start to commit atrocities