Kim Stanley Robinson dealt with violence on the left in his last novel - Ministry For the Future - which includes eco-terrorism in the struggle to deal with climate change. When asked about it, he admits that the novel has instances of violence, which raise these questions. But he says that:

"This novel, I hope, wasn’t making judgments that one thing is good and another bad. My feeling is that violence against other humans creates such anger and resentment that the backlash against it means terrorism doesn’t work."

Emma Goldman answered a similar question when interviewed in 1908. She replied that:

"But you know the pain and hardship it costs a mother to bring one little child into the world. I do not see how this complicated child, Society, is to be brought into a new being without pain and hardship. . . . I by no means prefer riot and bloodshed and death. But anarchists are not passive spectators in the theater of social development. And through all the ages the spirit of rebellion has been the spirit of progress."

The bottom line is that we avoid violence at all costs. That is the difference. We do not seek it or glorify it. But, I think of my cousin's husband, who was one of the leaders of the Warsaw Ghetto Uprising. I don't think I could do that, but I don't blame him either.