I watched a programme recently on psychopaths and what makes them what they are. According the programme some people are born without empathy. They are genetically born like that, and it is nurture that determines how they will grow up. A bad and violent childhood is likely to turn these people into murderers, and a calm and loving childhood would make people who end up as very successful movers and shakers of industry. The ruthlessness is directed in either positive or negative ways depending on the individual and whether they have learned how to function in society and learned to care about others.
In the programme they said that soldiers have to be trained how to kill because the majority of people find it virtually impossible to deliberately kill or injure another person. A person who is genetically a potential psychopath would have no problem at all with this, the only thing that stops law abiding and non violent psychopathic types from committing crimes is the fact they don’t want to get caught.
So, nature and nurture working in sychronicity defines the individual and evil doesn’t come into it at all. :D