This addresses my own concerns about what, exactly, is going on 'behind' the book. The husband you mention in your post - well, it doesn't surprise me that this is the type of family structure to whom the message of the book appeals.
People who can accept brutality (it's a bit beyond 'discipline' -- this is not a matter of 'discipline' IMO, anymore than it's about Christianity...) as a means of child control can also accept the idea that we ALL need to be controlled, starting from control within the family and working out, and violence is an acceptable way of achieving that.
It's all several degrees too cultish for me to feel easy about..