Well, if you recall, I never did come up with a satisfying explanation for why my Dad let people abuse me - which I would classify as hideous! He knew I was being abused on a daily basis, and he did nothing. Not okay, and not minor.

He's very intelligent. Money was not the issue. He has no disability or mental illness. He just didn't care enough. He had other priorities that were more important to him than my well-being. Plus, he told himself that it wasn't that bad, it was for my own good, some day I'd appreciate it, etc.

Awful as it is, that sort of situation - parent or parents who don't have a mental illness, but neglect, fail to protect, and/or emotionally abuse their kids, all the while making excuses to themselves - is actually fairly common. I think that was basically the case with Diana Wynne Jones' actual parents as well. You don't have to be a sociopath, you just have to be less empathetic and more selfish than is the norm.