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. Unfortunately, they are often least rational at those times, so calmly explaining things at such times is problematic, to say the least. TCS is an untested theory that places an impossibly high level of expectations on the parents and leaves them with a high level of guilt for not doing it right, along with a lack of practical tools for dealing with the inevitable problem situations.