Goal Hadam -- I would suggest that one component is the help atone for the murderer. He was careless with human life. Now, he will need to live in constant fear of death and always be mindful that his actions may jeopardize his life. He feels that his murder was a accident, or somehow necessary. But if the other's life was precious to him, he would have been careful and avoided it--as he is careful with this own.
In addition, this creates situation of house-arrest that is self-enforcing.
Note, that there is a dispute over whether the Goal Hadam is encouraged to avenge his relative, or only exempt from punishment for doing so.
