its bad science. I can name zero times when the victim reacting with aggression in an effective way (i.e. hurting or shaming the bully) did not result in better behavior from the aggressor in the following confrontations. I have worked with children and adolescents a lot of years and people standing up for themselves are usually better off.

Now, there are some side notes: the standing up must be timely and appropriate. The revenge shouldnt be served cold and the revenge shouldn't raise sympathy for the bully.