Are there people born evil? I don't think so. Ever seen a picture of Adolph Hitler when he was a tiny baby? Looks like a little angel. What sort of upbringing did he have to turn him into the 'monster' he was to become? What feelings of inferiority drove him to seek such power?
I would suggest that this was done by environment. Environment engenders thought, thought engenders environment; each is cause and effect. So you can well imagine that a little tot who is constantly subjected to a lack of love will turn out to be an unloving child and, eventually unloving adult.
So it isn't just a matter of parents being indifferent, cruel, calous and perhaps even sadistic, it also involves the thoughts of the child who is being subjected to this. If you can call such mental and emotional reactions thought.
A child has no idea that they are 'not their thoughts.' Indeed, a lot of adults go through their entire lives not realizing this. So thought begets thought begets thought, and the response is that more and more fear, hatred, and feelings of separation are layed down in the mind of such a victim (for they are victim's of victims - their parents probably knew no better) until we have a person who we would call 'insane.' That is, they have lost all feelings of human belongingness. They are, to use the biblical term 'cut off from the vine.'
So the opposite of love is not hatred, or madness, but a condition far removed from the love which is our essence. Its basis is not evil but fear.