I've been doing some research into the long standing philosophical debate about evil and why it exists and where it comes from. And I was going to come on here and write up a long post about my views on evil and attempt to use all sorts of logic and common sense to make my points. Then I realized something. The majority of the world's population, or at least the people I deal with on a daily basis, have no logic or common sense. I believe that's where evil comes from if it does in fact exist. If everyone had logic and common sense I would think it would tell everyone that living peacefully with everyone else would be preferable to living in fear of being attacked by aggressors. So therefore if no one were the aggressors most, if not all, man made evil would cease to be.
Sadly, while it is possible to teach logic, most people seem unwilling to learn it, preferring to live passionately and let their emotions rule their actions. And while it may be possible to teach logic to those willing to learn, common sense is something that can't really be taught.