Necessary and unnecessary violence is subjective. For instance, for a butcher, hunting or a killing may be necessary. How does one deal with this subjectivity?   
There are certain principles that are universal. Violence will always be criticised. Violence first hurts our own consciousness. Our own mind gets contaminated by negative thoughts. It’s a fine line to find out what is necessary and unnecessary. Each individual has to choose. Everyone has a choice, so ask the question to yourself and listen to what your consciousness says. What your consciousness speaks is the right action for you to do. 
If you hear the voice of your own consciousness, you will get solutions to your problems.