In mathematics and statistics, the term arithmetic mean is preferred over simply mean because it helps to differentiate between other means such as geometric and harmonic mean. Statistical mean is the most common term for calculating the mean of a statistical distribution.
There were, in my opinion, two main reasons for this: 1  I believe that Dr. King believed that nonviolence was a more moral strategy than one that included violence. 2  King also believed that nonviolence was a more effective way to get people on the side of the protestors.
1 From 1955 until his death in 1968, Martin Luther King Jr. was the dominant leader of the US civil rights movement. Following the teachings of Mahatma Gandhi, the Rev. Dr. King believed that nonviolent protest is the most effective weapon against a racist and unjust society. But it required rallying people to his cause.