Well here's a piece from a book I just read:
On the most fundamental level, my sense is that we are a kind, compassionate, and caring species,........At the same time, out of necessity, we are also a species of warriors and survivors. When driven to extremes, we have the power, capacity, and will to override our fundamental nature and become violent, to protect and survive. Our violence can be triggered by circumstances, either real or perceived, that we believe threaten us as individuals, families, communities, or nations. At other times, we strike out in acts of sheer desperation at circumstances that seem beyond our control. Regardless of the reason that we betray what has been called our fundamental "goodness," it is in such moments that we witness the very worst and most frightening aspects of our nature.
In the absence of conditions that drive us to be animal-like in our actions, a growing body of ancient, scholarly, and scientific evidence suggests that when given the opportunity, we prefer to live peaceful and considerate lives that honor the benevolent aspects of our species.
What he goes onto talk about is that people are generally "good" by nature.
Now when Jesus said "those who live by the sword will die by the sword", IMO, meant that yes, if you fight, you usually die fighting. There was no "wrong or right" about it, but it just IS at times. Meaning, people do what they know and then when they know better they do better. I think we live in a time where there is a shift taking place among mankind where war, is just NOT working hence we wont need a military. It will change, I really believe that. And again, for me like everything else, it goes back to motive. Idk, just my thoughts.
PS were you in the military??