I think what snood meant ( correct me.. ? )
is that not everyone knows HOW, or are able to overpower someone to do so.
Given the means, ( gun in hand ) yes... I do believe that people will kill if need be.
Of course every human being has the 'ability' to kill.. it is a survival tactic.
It has been there long before we told people not to do it anymore.
It is a natural part of our makeup.
The question is why, how, when, where do people act on it.
We all 'know' you dont NEED to kill people.. we all KNOW we should not kill people, yet some do. And enjoy it..
that is where your 'why' question should be.