In a comment below, Steven Riddle alludes to an important phenomenon in discussions on nonviolence -- viz, that the term means different things to different people. In particular, Steven notes the
Gandhian sense of nonviolence, which perpetrates on its own a whole series of violences that are unique in their brutality. (Not giving a person an injection of a much needed anti-biotic because it represents violence to the body, so that the person, in fact, dies.)
As I suggested in a subsequent comment, Fr. John Dear, SJ, seems for the most part to intend "nonviolence" in the literal and narrow sense of avoiding physical acts of aggression against another person.
Which is fine, but then what term do we use for psychological or spiritual acts of aggression against another person? For that matter, why privilege acts of aggression against another person as the only relevant sins?
Far be it from me to criticize the categorizing of sins in illuminative ways. But if you're going to use your categories as the basis of a moral code, they have to cover all the acts you want to proscribe.
And in the case of those who want to proscribe violence, I might be more convinced of the soundness of their moral code if they were soundly nonviolent themselves. It's certainly possible, and possibly useful, to distinguish between physical violence and passive-aggressive sanctimony, for example, but I don't think it's very sensible to condemn the former in the spirit of the latter, which seems to be common among those who preach nonviolence.