See this is what I'm talking about though you're acting like they're Humans who just suddenly went on murder sprees and not literal monsters that are brought into a world where they're instantly put at violent odds with Humanity.
That's the thing though. They *are* monsters. Humans, to them, are nothing but food. You could take the route of befriending them, sure, but you're befriending
one of them. Barghests, Lampases (Lampi? Whatever the fuck the plural of Lampas is), and Camazotz are entire species. That's an entire species that still goes on to hunt down and kill people. Arguably, being caught by a Barghest would be one of the best fates to have. They just rape you and steal your soul. A Lampas rapes you, steals your soul, and turns you into a fucking lamp, sticking you with her forever. A Camazotz parasitizes you, making you a prisoner of your own body. That's fucking horrifying to think about.
Just how many do you think they've killed? How many do you think they'll keep killing? And that's not even getting into the ones who you can't befriend like the Harpy Spawn.
And again it feels like you're missing the point to just justify some weird attitude toward the game when you don't really need to because if you spare her she either kills herself or enters your mind in a way where she isn't actually able to ever leave again unless it's seemingly to help you.(Remember in the mercy ending you're explicitely told they're always going to reside in some unconscious your mind as a consolation if you give up your magic implying they can't actually leave and the only time you ever see any monsters leave your mind is when they help you out.)
Honestly, I'm focusing on all of the demons, not just Arachne. For her though... Alright, explain the post credits scene of true mercy. Or it might be before credits, can't remember. How is she outside of Kazuya's head in the real world? Does she not explicitly state that she's going to go out to catch and eat more people, and invite Titanoboa to come along with her? Explain her marriage scene. Does she not state that she's going to continue catching and eating people, and that she's waiting for the right time to eat you as well?
Basically the point I'm making is it's just kinda weird to me like you all could just go I like genocide route more because it's more interesting/fun it doesn't have to be some sort of "its the 'objectively' morally correction option".
I... really don't think I had fun with this game at all, as weird as that sounds to say considering my activity in this thread. I just got into it to pass the time. Enjoyed it a bit, yeah, but when you actually look at this story you start to see it for what a fucking trainwreck it is.
Tell me, how is it not right to act in self defense? Demons will hunt down humanity until they are all gone. Hell, they can't even be killed (most of them at least), just sent back to the demon realm. How is it not morally correct to prevent humanity from going extinct by removing an obviously extremely hostile, completely remorseless force?