I am not quite understanding the question, either.
Whether or not you consider the statement to be true is a matter of opinion and the degree of the injustice. It took 100 years to get the Civil Rights Law of 1968 passed, while the main form of protest was nonviolent passive resistance. Mahatma Gandhi manage to get independence for India in a few years by nonviolent means. Although the Boston Tea Party cannot be classified as violence, the Revolutionary War that followed was considered a violent rebellion by the British.
That social injustice does not justify violent action?
I'm not exactly understanding what the question is asking. Any places where I could get info for points to back up this statement would be appreciated.
3 answers
Martin Luther King's march into Selma was definitely NOT violent and was a protest against social injustice. However, there were violent protests in Los Angeles and other places.
The violent protests in L.A., Detroit, Chicago, etc. tended to set back the Civil Rights cause. In the long run, it was the non-violent Civil Rights methods that won over the country to get rid of this form of social injustice.