I mean, the basic tenant of Christianity isn't about morality. Contemporary society turns Heaven and Hell into a "For the good", "For the Evil" type place like the Greek Underworld or some shit, but that's not what Christianity does. They say that no one deserves to get into heaven. Their actions, their words, nothing matters, because they're all evil. It's just that God loves everyone, so he's willing to let them off by having tortured himself for some reason. But yeah.
Anyhow, I'd imagine if I was God I'd do a lot differently, like A. Not letting people be born with psychopathic tendencies, so dealing with serial killers would never be something I'd have to face and everything would be great always. However, I doubt that's the answer you want, so instead we'll go with "What if I was an Anubis-type judge picking who goes to Heaven and Hell" rather than a God. I actually had a discussion like this the other week.
In practice, we punish serial killers for two practical reasons, ideologies aside: As a deterrent and as we can't let them roam free and continue killing.That's why I support locking criminals up when they do evil shit, because for society to function, we need to, we can talk about justice, but that's a metaphysical idea, and if we go into philosophical shit, we're kind of fucked for the following reason:
Really, we start off as babies, pure and innocent. We develop into serial killers either due to nature or nurture. Nature isn't our choice, as we don't pick to be sociopaths. Nurture isn't our choice, because we don't pick to be abused. You can't really blame anyone for their choices to any degree. If any of us were born with the same brain connections as Ted Bundy in the same family, we'd become a serial killer so at that point. Ultimately by that logic the only moral thing to do is let everyone go to heaven, as they never decided to be evil and thus we can't blame them for it. Otherwise, the system is just like End's, a game of absolute chance, only instead of a coin flip, it's where you're born and how your brain functions. Still, I think anyone who reads that will know it seems wrong at our core to not have ANY justice. Our reptilian brain wants justice, so I don't really want to send everyone to paradise for ever.
Ultimately at my core, I feel like heaven and hell seems like a shitty false dichotomy. No one deserves eternal paradise after all the pain they've caused, but no one deserves eternal punishment. Ideally, there'd be some sort of scheme where you're forced to feel every harm you intentionally caused another sentient being a few times, until the person truly understands the gravity of their actions. Then once they come to terms with that, let 'em off into paradise. It might not be as moral as sending everyone immediately there, but it's an idea that satisfies both halves of my mind, so that's my choice. Fuck it though, if that's not an option and I'm sticking with the dichotomy, just send everyone to paradise and let my lizard side stew in annoyance.
Probably not pure bliss paradise, more like a perfect version of Earth where you work for a bit at a job you like, face and overcome adversery and everything's pretty good.