perhaps they might not "like" to...but get them in a group situation , and anything is possible with the right stimulii. Adversity or perceived adversity can make even the nice as pie folk resort to things not normally undertaken, which some folk might see as 'evil".
Exception rather than the rule? ...perhaps, but the potential for violence and 'evil" ..is but a whisper away. I think your optimism is commendable ...but your naiievity, somewhat blind. Remember...even a killer can be an optomist ....and a saint a pessimist.
Cynicism?...or observation?..you choose.