There is still killing amongst a species.
for food, water, and shelter (and like Camera mentioned, to ensure reproduction)
you can argue that other animals do it all day if you want, but nothing you can say will make purposeless murder justifiable
not to mention that you're lying
given a gun, axe, or whatever the forget you want, and told you could kill an innocent man, you wouldn't do it
you wouldn't be
able to do it