Regarding the violence question, I cannot think of any animal on earth that when needs are met, are violent. Humans can conceptualize and realize needs that exceed those rationalized by animals lacking our cognitive abilities, and therefore experience scarcity based on expectations rather than physiological need. I do think that scarcity of resources is always the motivation for violence, even if that scarcity is psychological scarring from childhood abuse eg. Persistent lack of nurturing emotional input due to childhood emotional abuse.
Yes, I deem killing in self defense as a necessary event, though even under distress I shoot to stop the behavior, if death results, that is an unintended consequence. Is there ever justification for premeditated murder IYO?