I still feel like the dev should have given the monster girls more of a "neutral" morality if they wanted to get people to play non-genocide and have that be the bad ending. I played true mercy cuz that's just what crpgs have kinda taught me but I feel like the monster girls were all too apathetic or evil about the carnage they unleashed.
Your first point is a good idea.
I'm pretty sure it IS a marrige thing, just not in our human sense, i mean, lampas litteraly fuse with you, barghest are just dogs in heat, echo litteraly wants to 'love' you. Mother rabbit is a sort of inbetween because it isnt really marrige but parental affection. Mukuro is similar aswell, i'm not sure how much she loves you but her obessions is rooted in her own loneliness, rather than love towards you, but still close enough.
This alone doesn't fix anything, just because they like you wouldn't excuse what they do.
But as you said, then comes along the element of them being able to materialize the souls they claim.
This would completely eliminate alot of issues with what they're doing, it would very likely STILL be rape, but it actually makes the circumstances of their "killings" murky, did the men who "Died" give their consent? Were they coerced? There would likely be many who wouldn't, there might be some who do under coercion of their own free will.
This cartaintly opens the door to coexistence. (Even though the demons are invaders who shouldn't be in the human world in the first place)
It improves the demon's track record, but doesn't really erase it, rape is still a crime lol, not to mention the actual flesh eating ones.
Your second point is very bad, like really bad.
Trauma doesnt justify anything, absolutely nothing, you killed innocent people and that's a fact, whatever you experienced at the hands of x thing doesnt justify anything that you do.
But it does make actions more coherent, rather than a simple "i just wanna milk dudes" motive, but given that the demons are the invaders, it doesnt really make sense that their trauma (very likely caussed in the demon realm, which humans had nothing to do with) would justify your actions.
For someone like Camazotz, putting loneliness aside cause that doesnt change anything, their short life spans gives meaning to their madness, which may be able to rule out the fact they arent openly malicious, but their actions stay the same
Your 3rd point would never work, unless the mental age of every girl regressed to childhood
The concept of death can sometimes be undersstood by older kids, and almost guranteed by teenagers even without explanation, so it can't proerly be implemented without being forced.
You did good in trying to improve the very shitty moral compass of the game while still sticking to the original premise, but in my mind, i would still do the geno route without question.
Ignorance and trauma doesnt absolve you of any crime, it's still manslaughter at best, and even with the first point, you still DIE and likely get raped, only to be materialized again by your killer, that's not a good scenario to live in at all, i doubt anyone would actually be happy like that, sure, you can keep living, but like daji said, yuuma still has to fulfil his duties as a summoned creature, and she said that like he should be thankful or something, even though we didnt blast her into nonexistence and she just killed yuuma.
You NEED to keep going
DEMONS WILL try to stop you
Doing so results in your DEATH
and with the addition of point 1
They may or may not let you live again if they like you
You see how this looks like? in some ways, it's even worse than the original game lol.
The game needs to be completely rewritten at the base for geno route to actually be a villanous route, otherwise, it just doesnt work