Violence is absolutely necessary to be carried about by the righteous to keep the evil at bay. Man is inherently sinful. No amount of people asking and hoping for world peace will prevent evil people from wanting to carry out evil acts.

The point of "Be peaceful, not harmless" is for righteous individuals to conduct themselves in a peaceful manner at all times and at the same time have the capacity to exert violence, also at all times, in order to prevent evil from being carried out by evil people.