Responses
I'm betting it's a bullshit ends justify the means situation. Maybe they can only kill stalker god if it has a physical form. So if MC loses everyone he cares for/who cared for him and becomes broken enough to give in to the stalker god, he'll become a Big Bad and then they can kill said Big Bad and save the world! And everyone who gets murdered along the way is just lolwhoops collateral damage.
If Baek Young (and whoever is the God behind her) hated Seo Gangrim so much, why didn't she kill him when he was a kid? Instead she killed his parents, let him live depressed and alone for years, and when he finally made friends and comrades, she slaughtered all of them too before she finally killed him.
Was there a reason to make him suffer so much before killing him? It's like they wanted to break his spirit and make him as desperate as possible before taking him.