I’ve always been neutral to left on the “discipline” debates. I have always believed that there was something inherently wrong with most, if not all, corporal punishment.
On the other hand, corporal punishment does have something in common with self-mortification. And, sometimes, when it’s an emergency, a spanking can be the only viable way to teach the child that “this is danger.”
But still, spanking in anger is definitely wrong, and I’ve always seen it as a sign of defeat. It says, “You’ve overpowered me, kid, and now I’m lashing out at you for damaging my pride.” It encourages a power struggle between the parents children.