Occupy Wall Street is similar to many movements in contending that its opponent—for Occupy, the 1 percent—is maintaining a system whose structural, systematic violence far exceeds any violence exhibited by the movement itself. For example, movements will say that class oppression or sexism or racism hurt people in the daily course of life, pointing to statistics like each percentage point of unemployment resulting in increased suicide, homicide and domestic abuse. However, especially when the movement is still young and only beginning to get its message out, the powers that be in politics and the media will often succeed in dismissing such charges and in blaming every appearance of violence on the campaigners. Reversing this narrative in the public perception is one of a growing movement’s most important challenges.

For nearly a year, for example, the Syrian government has been sending its tanks to kill demonstrators while claiming that the violence mainly comes from the pro-democracy forces. The Russian government publicly agrees. The reason why defenders of oppression the world over charge activists with violence—even if they have to make it up—is because it’s a potent accusation. The oppressor doesn’t want the “violence” label to stick to its own side. Those who presently are undecided or passive might move to support the campaigners because they don’t want to support “violence.”

In some circumstances, although not all, who wins the struggle depends on who most believably asserts that the other side is violent. Occupy Wall Street ...