This does not mean that we justify violence and the oppression of others, but that we must understand that the only truly helpful solution consists in practicing beneficial acts in our immediate environment, and dedicate the merit to all who suffer —without excluding those who commit negative acts.
We have a special responsibility toward those beings in our immediate surroundings (our neighbors, human and non-human), since they are evidently linked to us through intimate karmic bonds.
If an act of violence against another being occurs in our presence, and we can prevent it without causing greater harm, we should attempt to do so. However, defending others should not lead us to develop aversion for any being, whatever his or her actions.
In this world of duality and suffering, there will never be true justice, or perfect happiness. The best we can do is to abstain from contributing to the suffering of others, perform beneficial acts, and dedicate the merit of our practice to all beings.