The collective bullying of a worker is called "mobbing," and it typically ensues when a worker does or says something to annoy management, and management declares or demonstrates that the worker is unwanted.
I can appreciate the difficulty of presenting social science research to a general audience unschooled in the data that have been examined and the techniques employed to examine the data to arrive at systematic results. Just as it would have been absurd for Zimbardo to get rid of the bad guards in hopes the aggressive behavior would be stopped, getting rid of the bullies in an institutional setting that has ignited and encouraged mobbing is an impossible task, given the number of aggressive participants.
In order to maintain a feeling of consistency, and to relieve dissonance regarding the conflict between my attitude and actions, I've convinced myself that my husband is an exception to the rule.
Andrew is experiencing Social Dominance Orientation, which is having such a strong desire to promote the dominance of your in-group that you adopt new values to promote oppression of other groups to increase dominance.
When that happens, it takes little effort to persuade the broader workforce to turn against the worker. Even among those guards who initially resisted the aggression, all eventually rationalized their decision to join ranks with authoritarian guards, and all soon rationalized their behavior as legitimate due to the behavior of the one being punished -- even when the one being punished had clearly done nothing wrong and the punishment was by any standard a violation of human decency.
It sounds like his mother must have hated him. I find this easy to relate to the use of steroids. So Claire discriminated against others to make herself feel better. This reality causes great dissonance, and thus motivation to explain what occurs in a different way. Although worthy, you cannot make that commitment, so you refuse because of the time commitment.