Back when I was teaching yoga in NYC and authored a yoga newsletter I thought and wrote about ahimsa, the practice of nonviolence. Some say that if one has a pure intention than they need not concern themselves with outcome. The trick to this kind of thinking is that it requires that the person with the intention be a "complete human being" capable of reflection and reason and with a fully working emotional body. Sadly this kind of person is rare. It has also been suggested that the practice of ahimsa is one created for the manipulation of the masses, to keep people from rising up against authority. Be that the case or not humanity has and will always wrestle with the question internally, "am i willing to be violent towards another life?" Many look to the natural world and its inherent violence. Here they find justification for violence.
While I still find this concept perplexing I have dug up a few morsels that I think are of value to me. What appears as violence in the natural world is more truly the process of life feeding upon life - life sustaining itself through itself. Violence in this form masks what is actually happening - a mutation of forms and a continuation of life at the cost and to the benefit of life.
I also feel the question is being asked backwards. We need ask the question from the position of how we choose to live our lives each day rather than from the "what if" position. If we choose peace and harmony than we will respect life and preserve it in all its forms as a practice. The practice itself tunes our hearts so that they serve their function of authentically feeling and experiencing the world with sensitivity. These hearts can respond appropriately to the world. Perhaps, as suggested above, they can act from intention with less regard for consequence? Unfortunately all of our hearts have been tainted by the world we live in. Do you cry when you read the newspaper or watch the news? Daily heart practice invites the heart to remember its function and through it we regain a sense of awe for the beauty inherent in the multitude of living beings.
If the moment should come that we must decide if we will use violence to defend ourselves, a working heart will be more likely to make a decision that is in tune with with the greatest kind of knowledge, that of the heart. Surely the inversion of this argument has been made obvious by our culture. Immersed in needless violence through media and war we have come even to choose violence as a form of entertainment. Our culture chooses violence by default. It produces people who are numb to violence and so ever more capable of tolerating it and creating it.
This may seem an awkward place to post a photo of myself at the shooting range. I can not say how I would respond given the situation of self defense. I will prepare myself by knowing how to shoot a gun. And I will rely on my tuned heart and work on it every day so that it will lead the way if a decision is at my door. If our society were to choose to cultivate its collective heart than we may not find ourselves facing these kinds of decisions at all. A daily heart practice sets in motion the greatest possibility for a genuine life lived one that feels deeply and knows the world through empathy and awe.