It's true that 'good' and 'evil', what's right and what is wrong, is all defined by society. Upbringing is the crucial part of it all.
A suicidal extremist, raised to kill,
KNOWS that they will be welcomed into the afterlife after murdering as many people as possible. So they willingly do it. The average person, though,
KNOWS that this isn't so - although some still cling on to the idea of heaven, they don't see murder as a pathway to it.
So, we are not born as anything. The only way you could be born as a killer is if you had a serious brain defect and could never integrate yourself into the world and learn morals, but most/all such people wouldn't have the ability to commit a murder anyhow.
The important thing is to keep an open mind, even on the most sensitive topics. "Always stay out of your comfort zone, or you'll only ever find what you're comfortable with. And that's a long, boring waste of life." - Me.
how could it develop if human beings did not have the notion already embedded in their minds (albeit undeveloped)?
Morals and religion developed because a caveman at some point in history saw a way of controlling the masses to his benefit. Unfortunately, the world we live in is still heavily based on this concept, and realistically always will be.