A colleague of mine, years ago, took a job as the healthcare manager of the Santa Monica Free Clinic (he's an anthropologist). Many of their patients were mentally ill.
He wrote a really poignant article about how people who are acutely upset and suicidal (a common grief reaction), could readily flip and become homicidal instead.
I can't find the article for some reason. Anyway he mentioned that he erroneously thought that "loving" or "caring" for a person who was suicidal/grief-stricken would surely help them.
A member of the staff not a patient was grieving and suicidal, was getting psychotherapy and, my colleague gave him kindness, love, compassion, etc. There were so many depressed patients, my colleague thought that trying to cheer this man up, be his friend would be the antidote
The man frequently expressed suicidal ideation. Then, one day, he came to work and shot up the clinic, killing 2 coworkers and injuring several others. This was not the shooting in 2013, so I'm not doxxing anyone.
So the anthropologist wrote this piece and he said:
1) everyone knows that murder/killing humans is taboo. It's a human universal and everyone knows it, except perhaps the severely incapacitated mentally ill - who are too disorganized to buy weapon and ammo (as this assailant did).
2) Willingness to kill oneself and thinking about killing oneself still breaks the tabu and indicates a willingness to break the tabu.
3) Once a person is willing to kill humans, they are willing to kill both themselves - and others.
Some kill others first, intending to kill themselves (or suicide by cop). Then, they are prevented from carrying out their "kill others" mission and never quite get around to killing themselves.
In jail, this assailant told my colleague he still very much wanted to kill himself. He had always wanted to kill himself but somehow, after acquiring the means to do so, he thought he'd also take out a few people who had "hurt him." In other words, a person willing to be so aberrant and living so much in the belief that "soon it's going to be over" (for someone), is very dangerous.
Even if Albert had tried to get help for LS or treated her with real concern and compassion, it probably wouldn't have helped, especially if he was thinking of leaving or there were other issues (she dreaded him finding out about her real employment prospects). He says he "gave more to her" than to any other woman. He tried the supportive route.
This was before there was much literature about extensive suicide and to me, has always helped explain the actions of the people who kill family members or their whole family and then either kill themselves OR stop because their own self-preservation instinct is still there. They wanted to die, to "end everything," and their mind embraced violence, conceived of how to kill, thought about dying and killing, and they never "meant to" kill their families and not kill themselves.
LS filled up with hate. She wanted to "end everything." It's possible her mind darted around, hating Albert, hating Gannon, and perhaps occasionally even hating herself - but we know she was incapable of just killing herself (if divorce was so unappealing due to her intense fears of failure and abandonment). I totally agree that "winning" Albert away from Landen gave her a kind of high; that went away after a while and she was left in her same old state (I'll bet quite a bit that LS does occasionally have moments of self-loathing, but probably not for the reasons the rest of us would).
Sorry for the very long response - but it just seemed to me that you intuitively knew all of this. And our parents knew it too, which is why we were strongly discouraged from hating, using the word hate, lying, lashing out, harming others, etc. Even well brought up adults can break the tabu, but if tabus in general are broken (and there are many), the child learns to be a kapu/tabu-breaker.
Children need to learn how to love, how to deal with discouragement - and how to deal with disappointment or anger without killing people.