OK, I'll take a hack at it... the following will exclude psychopaths and such. I''ll avoid the terms good and bad.
We are born with compassion for others and attraction to others at the surface of our personality. Babies are not hateful, at least not right away.
As we grow older, events occur that we associate with threats to us - real or imagined, physical or emotional. We adopt behaviors to keep us safe from these threats. We shut down emotionally, we decide that men or women are always going to hurt us, we decide that the world will take advantage of us. Some of us lash out first to keep people away so that we won't get hurt after they get close to us. In this way we cover up the compassion and attraction that was originally there.
We continue these behaviors for years, even after the threat is gone. Habits and reactions learned young are hard to shake.
Much of the pain and hurt inflicted on others, much of the anger in the world, is anger carried around from childhood that never had a place to go. I'm not minimizing crimes committed by "rehabilitated" criminals -it's much easier to identify the anger than to change our automatic reactions.
I believe that fear -fear of being unloveable, fear of being rejected, fear of being alone, and fear of not being good enough on one's own - fear is what keeps most people in the WTS, and fear is also why most humans hurt others. It's only after we conquer our fears that we reach out with compassion.
Every day man is crucified between two thieves - the regrets of yesterday and the fears of tomorrow. Benjamin Disraeli.