Moral matrices bind people together and blind them to the coherence, or even existence, of other matrices. This makes it very difficult for people to consider the possibility that there might really be more than one form of moral truth, or more than one valid framework for judging people or running a society.
It is very tempting to take the side of the perpetrator. All the perpetrator asks is that the bystander do nothing. He appeals to the universal desire to see, hear, and speak no evil. The victim, on the contrary, asks the bystander to share the burden of pain. The victim demands action, engagement, and remembering.