Clearly Defined roles?

I don't think good and evil are 100% defined, simply because evil people can do good things and good people can do evil things. To make this statement more clear, I can start off by illustrating some examples. When an evil person does something good, we should question: what is their purpose of the act? Likewise, we should ask a good person doing something evil: what is the purpose of what they did? In some cases, the action may not be deliberate or it may be done, knowing full well what the person was doing.

Realistically speaking, i doubt very many people would be 100% good. Just imagine if people listened to everything that every single person said, aside from constructive criticism or important things to improve yourself. That would mean that if someone says to go jump off a bridge, you would listen and jump off. A good person doesn't have to go to that extreme where, they do exactly as everyone tells them to, but they should be able to think of the greater good and think for themselves. Some people may seem like they are 100% evil by horrendous crimes they may have committed but who's to say behind closed doors, they can't live with themselves? Even if it is a bit of remorse of some sort, they still have a bit of goodness inside of them, its just overpowered by evil. In that case, an evil person would have to posses qualities or do things primarily evil, even if they do a few good things.

So if someone was 100% good, and listened to the letter of every person's word, it can cause some trouble. Same thing is someone was 100% evil, its obvious that they would have no remorse for evil actions, can live with themselves and they are pretty much a programmed machine, with no feelings. So you can achieve the same effect by having too much of one side. Without evil there is no good but without good there is no evil.