The rebels in war-torn countries get new recruits by a nasty, nasty cycle.
First the go to an institution of education. A school.
Then the shoot it up. They say you can join them, or you can have your hand cut off. They cut off your hand so you can't pull a trigger on them later on.
If you join (which most young, self-preserving children will do) they take a shank and put a knick in your head. Then they smear in a combination of gun powder, saliva, and cocaine. This drives the kid wonky.
They are then given a choice: they can rape their sister or kill their parents.
Then they burn down the school and ride off (with their new poor souls) to perpetuate their cycle of violence.
...
About good and evil:
Nope, not real. Humans, being social creatures, are somewhat genetically programmed to think that acts which aid other members of the species (/ group / family / etc.) are 'good' while acts which don't are 'bad' or 'evil.' (Think about it - how else could the early cavemen have survived? In an every-man-for-himself environment filled with harsh elements, nasty predators, no good self-defense mechanisms but a big brain, no one lasts long. Even the people smart and lucky enough to make it wouldn't get to reproduce, so their genetic material doesn't get perpetuated.)
As such, you then take what you've learnt (your own personal experience) and mix it with this subtle programming to build up your beliefs about 'good' and 'evil.'