When you speak about injustice, you do not see the karmic relation to the situation, the relation start in the past and what you experience as injustic is the result of the karma that is re-payed. One does not need to have hate or anger rise within when seeing this, but when one have compassion it is ok to try to end the situation in a calm and good way. But as an example if you see two people fighting in the street, we can not know the cause of the fight, it might be karmic relation from earlier in the life of the two people. so should we stop them? not if you do not know the cause of the fight. (karmic law) if we stop it now, it will sooner or later need to be repayed.
To not hate someone because of their action toward you self or others, one must have compassion arise within , when compassion arise one will feel sorry for the person who start the fight or argument, instead of getting angry our self, we can stay calm