1. Fear: If a Bear approached you in your yard, would you embrace it and be kind, or use some type of defense mechanism? Most likely, you would attack or run.
2. Hunger: If the animal does attack out of hunger (which is unlikely) it is because that animal sees you as you are - another animal. Non-human omnivorous/carnivorous animals have not yet taken to gardening nor can they analyze animal rights philosophy, and human occupation of their lands is making it a great deal harder for them to find food. My point is, animals interact with the world instinctively and with a different type of intelligence than humans do. Let's not fail to note that humans have been known to eat humans under severely strained circumstances (that's not including psychopathic behavior).
3. Let's be honest: Veganism in no way states that a person cannot harm an animal (human or non-human) in the case of self-defense. But when omnivores eat animals, it is only for tradition and personal enjoyment, not self-preservation. Cows, Pigs, Chickens, Fish, etc. are bred and tortured for nothing more than fun and enjoyment...
ANIMAL PRODUCTS ARE NOT NECESSARY FOR SURVIVAL!