If animals kill, we deem it to be innate...
If humans kill, we deem it to be either accidental or intentional, and instead focus on intent (self defense, war, anger/fear, etc), and assert that killing is in no wise innate in humans...(with certain exceptions...)
Humans are animals. Therefore, humans killing is innate...
or,
Humans are special animals--or are not animals at all--so what we observe in the behavior of other animals doesn't apply to us. Sure, there's accidents and self-defense (just as appears in other species)...but otherwise, human nature is not to kill, and therefore it is a learned, and therefore unnatural, behavior...