Furthermore, children vary dramatically from day to day and from hour to hour in their capability to reason. The right response at 5pm may be very different from the right reponse at 10pm. Indeed, the best way to teach is by example. But children, like adults, are at varying stages of ethical development. Learning that inappropriate behavior leads to bad things happening, even from parents who love them, is a useful lesson.
Parents do react.
They are going to display strong negative emotions. Some people scream, some people go silent. People are different and respond to different things. Also, they react differently at different times. In my observation, most behavior problems occur when kids are hungry, tired, or haven't had enough physical exercise to blow off energy.