Violence is necessary for peace and power
The violence that is used to protect an individual's rights is good. Violence is necessary because, without its threat, humans would endanger each other since there would be no consequences for their actions. Citizens of the world are grounded by criminal laws that are punishable by death or other forms of violence. Peace means the lack of violence, but it is the presence of the legal justice system and criminal laws that allow humans to respect each other and look out for each other's safety. The absence of violence or war doesn't mean that people will be free of repression, injustice, or psychological violence since the meaning and triggers of violence evolve with humans. For instance, Homosexuality was considered a pathological disorder, and something had to be treated. However, with the establishment of science, we have come to understand that homosexuality is not a disorder but rather a natural state of being. In prioritizing peace, many people would not want to disturb the laws and policies that might cause disruption. This is why the fear of violence in the form of justice is necessary to keep citizens peaceful. 
No matter what the reason is, violence is always wrong. There are moral ways of educating people on committing crimes or offending someone. Acts of violence only perpetuate further violence. Engaging in violence can never result in peace. It is a rage-reaction cycle, that will continue for as long as violence is present.