Killers/Murderers - Are they really wrong?

Right now humans obviously live in a society together aiming to learn about the world and beyond. Based off of the theory evolution, us and apes both have a common nature to dominate and use tools. Being that we are all either plant or animal, isn’t fighting for dominance the correct way to do things? Since we are animals (based off of the theory of evolution), and apes as well as many other animals fight to the death. Isn’t murder, killing, fighting, part of who we are inside?
Like other civilians, I dislike the view of killing and the loss of lives in others. Some may debate that society is there to make humans work together to reach a common goal, but it doesn’t appear that we are so focused on that anymore. Without fighting and war, the human population has no choice but to increase over time. It’s 2014, and our tools are getting strong, powerful, useful, and more dangerous. The thinking that once got us better lives are now making them worse in ways.
Sure there are people who are mentally ill, or angry, but are they really bad? Is there a reason to this madness, possibly a rebellion to society? What are your thoughts on this topic?

EDIT: I see I have made some mistakes with facts on evolution and such, but hopefully I got my point across.

EDIT 2: I didn’t think carefully when I said murder. Let’s just say killing alone.