Thanks very much for your comments, and for giving me my first post!
What you say about intimate cruelty being overpowering expresses a feeling many people have about cruelty: that it really does matter who's being cruel and to whom. Somehow, cruelty between people who ought to love each other seems exceptionally awful. Even looking at it 'dispassionately', if you like, from the point of view of evolutionary psychology (evopsych), it seems crazy to hurt or kill the people closest to you, who give your genes the best chance of survival. But people do.
Evopsych writers like David Buss argue that much lethal domestic violence can be made to make sense, because it's directed against the partner or stepkids -- who usually share fewer genes with the attacker -- rather than his or her own kids.
Maybe. But parents do sometimes kill their children, and cruelty isn't just about killing (although that is the extreme that most people, including me, focus on discussing). One suggestion as to why is that physical violence can be hard to calibrate, especially if you're already drunk, high on drugs or infuriated. Situations can escalate rapidly, and in a way which doesn't give a person's moral inhibitions time to kick in.
More speculatively, I'll go out on a limb (necessarily simplifying, I'm afraid) and talk about love and hate. When someone falls in love, among the many things that can happen is that the beloved becomes hugely important to them, such that thoughts about him or her start to make up a lot of the mental landscape, the psychological self.
One aspect of this is that new lovers often talk for hours, or try to spend a lot of time together doing the same things. They're finding and emphasising points of similarity. "He adores my favourite band!"; "She's the only woman I've ever met who understands the offside rule"; that kind of thing. They're downplaying differences and making their psychological selves feel more alike. This process, and the huge emotional importance of thoughts about the other person, makes them 'take over' a huge chunk of one's psychological self.
It's an empowering feeling, that there's someone who shares so much with you and feels like you do -- and from choice rather than because of genetic ties! When the bliss wears off, however, differences may start to emerge which can't be ignored or downplayed, especially if the couple is under external pressure (struggling with financial difficulties, for instance). That's a real problem, because closely bound selves aren't supposed to have important differences.
Anyone who is strongly committed to an idea (or ideal), and has that idea challenged, can find it hard not to see that challenge as a threat. If, say, Jane believes her partner loves her, and someone provides evidence that he's cheating on her, she's not going to sit down and calmly analyse that evidence. She's going to react as if she's under serious, immediate threat, right down to the muscle tension and racing heartbeat.
When we're threatened, one of the things we do is what in Cruelty I call 'otherizing': pushing the source of the threat away, making the person into an enemy. When people find themselves in conflict, they react in ways which make them feel less similar, emphasising differences they previously ignored ("I should have known, he likes hip-hop, why didn't I see the warning signs?").
When someone has been extremely close, that's even more threatening -- they know so much about you! That can make the attempts to push them away even more ferocious. Of course, they'll probably react badly to your behaviour. That just confirms your new perspective of them as hostile (and theirs of you!). Now they're well on the way to becoming an intolerable threat.
The result: a vicious circle which can lead to mutual loathing -- and violent cruelty. Being cruel to enemies is much more acceptable than being cruel to people one loves.
In my next post, I'll have a look at cases in which that cruelty leads to murder.