The more we understand about someone's life — about their family history, about the suffering they went trough as a child, about the suffering of their parents and grandparents, about the injustices done to them or their family, about how they or their parents or grandparents were exploited or abused — the less we can reject them because of the terrible things that they did themselves, the less we can push them away and consider them bad.
One of the great advantages of family constellation work is, that we look at what happened in the context of multiple generations. We try to look at the whole context that produced a certain behavior, or a certain event. If you look deep enough, you will ultimately understand any behavior, any act. Even if someone did something terrible, and caused a lot of suffering, you can look at it from a perspective beyond good and evil, where you are not interested to judge, but only to understand.
Family constellation work is about finding resolution for suffering that was produced by systemic family forces. If we look more fundamentally, those systemic family forces are just our instinctive social drives. Those social instincts are literally older than the human race. They are as old as when in the evolution of species, certain animals began to live in groups to increase their survival chances.
Our conscience is simply a social instinct that makes us feel bad when we have acted in a way that threatens our belonging to our survival group; it makes us feel good when we have behaved in a way that secures our belonging. And our morals are nothing more, then instinctive forces that want to include those who increase our survival chances and want to push out those who diminsish our chances. Judgment is simply the expression of those instincts in us.
Conscience and morals do not lift us above above our animal drives; to the contrary, they are our animal drives.
If we want to heal the pain produced by such instinctual forces we must understand those forces, and recognize when they are active in us. And we must find a perspective from where we can work with a person without judging them. And as said, it lies in the nature of family constelation work itself, to help us find that perspective.
The superego work that students are required to do, is a fundamental exercise to become non-judgmental. You first have to stop your self-criticism; then you can stop being judgmental to others as well.