The "ifs" are critical. Not that the use of power and authority is not harmful; the use of power and authority will be even more harmful when parents are inconsistent. Not that children want their parents to use authority; rather, if it is to be used they would prefer to be used consistently. If parents feel they have to use authority, consistency in applying it will give the child much more chance of knowing for certain what behaviors will be consistently punished and what others will be rewarded.
Considerable experimental evidence shows the harmful effects of inconsistency in using rewards and punishment to modify the behavior of animals. A classic experiment by a psychologist, Norman Maier, is one example. Maier rewards rats for jumping from a platform and through a hinged door on which was painted a particular design, like a square. The door opened to food and the rat was rewarded. Then Maier punished rats who jumped from the platform toward a door that was painted with a different design, a triangle. This door did not open, causing the rats to hit their noses and fall a considerable distance into a net. This "taught" rats to discriminate between a square and a triangle--a simple conditioning experiment.
Now Maier decided to be "inconsistent" in using rewards and punishment. He deliberately changed the conditions by randomly alternating the designs. Sometimes the square was on the door that led to food, sometimes it was on the door that did not open and made the rats fall. Like many parents, the psychologist was inconsistent in applying reward and punishment.
What did this do to the rats? It made them "neurotic"; some developed skin disorders, some went into catatonic states,some ran around their cages frantically and aimlessly, some refused to associate with the other rats, some would not eat. Maier created "experimental neuroses" in rats by being inconsistent.
The effect of inconsistency in the use of rewards and punishment can be similarly harmful to children. Inconsistency gives them no chance to learn the "proper" (rewarded) behavior and to avoid the "undesirable" behavior. They cannot win. They may become frustrated, confused, angry, and even "neurotic."*
*Excerpt from Dr. Thomas Gordon's P.E.T. book