Ahimsa (nonviolence) is the first moral principle that Patanjali presents to us in the Yoga Sutra, and therefore, ahimsa is the foundation with which we can choose to live and build our yogic lives around. What does this nonviolence thing entail?
How we think, act, speak, treat ourselves as well as others can be respectful or harmful. Does it really hurt someone to think bad thoughts? Science tells us yes, absolutely. Just look at the work of Dr. Masaru Emoto and how water responds to harsh thoughts and words.
Some yogis become vegetarians become because they want a lighter diet, for some it’s a preference and still others want to choose a non-violent lifestyle (not eating flesh because of killing animals). I have a number of yogi friends who are committed to a life of ahimsa (non-violence) who need to eat meat because of their constitution and/or body type. They can look for animals that have been treated humanely, say a special blessing acknowledging their gratitude for the animal’s life or find another protein source.
So what was Patanjali suggesting in Yoga Sutra 2.35, अहिंसा प्रतिस्थायं तत् संनिधौ ahimsa pratisthayam tat vaira-tyagah, says that, “When we are established in non-violence, those who come into contact with us will do the same [be nonviolent].” If I learn to think, speak, act and live a life without harming myself or others, those I come into contact with, over time, will do the same. The opposite who also be true. Violence begets violence and peace begets peace.