The majority of "evil" -- or just nastiness -- I think is less due to malice, hate, or cruelty.
I think the majority of bad things people do happen because they're (1) afraid, and (2) they take the expedient course.
Fear is a mess, of course. Scared people do all kinds of idiot moves.
(Which isn't to say that fear is irrational. Maybe the fear is justified. But scared people do stupid and crazy things.)
But fear... fear is probably okay, even. If you work through it. If you understand it. If you take time and work at it.
The nasty thing is when you're scared and you take the expedient path -- whatever the easy play is, whatever the first thing that springs to mind is. That's when people do quite a lot of damage -- when they're scared, and take the easiest, most expedient path towards feeling less afraid.
A corollary could then be GOOD = Long Term Strategy + Courage. (Not sure what the opposite of fear in that equation would really be.)
But yeah, from personal experience, it's not malice. It's taking the shortest route because someone was scared/unprepared. It's someone being unsure of himself, so he reverts to the most obvious, most established, or what he perceives to be the least risky action--regardless of the overall cost.
Courage is being scared to death... and saddling up anyway. ~John Wayne
Obviously John plans to charge, not ride the hell outta town. It can take courage to do what is right or necessary. I think you are right that evil can occur simply through inaction or taking the most expedient route.