MOO:
It seems to me that a lot of abuse is just a knee-jerk reaction of the parent when they're angry, even though it may have nothing to do with the child's behavior.
When the parent physically punishes the child, it's a release of their anger, which means it can actually start to feel good to the parent. So they do it again and again because, subconsciously, they know that release of rage feels good. Which can lead them to subconsciously come up with more and more spurious reasons to punish the child.
I can remember being physically punished for reasons that don't make any sense to me as an adult, looking back. (Of course, they didn't make sense when I was a kid, either.) Heck, some of the things I got punished for would probably have been rewarded by a saner parent.
A teachable moment requires the parent to be able to put a freeze on any anger they may have and instead calmly articulate the lesson they trying to impart to the child. There needs to be a societal expectation that talking about the lesson is the default first method of correction, followed by non-physical consequences that are assigned without anger.
Punishment stemming from anger is unhealthy for everyone involved.