Heros

"A hero is born among a hundred, a wise man is found among a thousand, but an accomplished one might not be found even among a hundred thousand men."

~ Plato

Good vs. Bad

"Are people good because they want to be? Or are they good because they are afraid to be bad? ... I think the good person will be no different from the bad person."

~ Plato

I agree with this statement as long as the situation is within reasonable bounds according to personal morals and the law. Essentially morals can only be broken if an individual holds them (and of course abides by the law). So, if that is determined then what about temptation? Does it get in the way of morals? Can it be said that selfishness does too? Why do we as humans give in to the temptation to be bad? I personally don't think that this is such a terrible thing. Being able to give in to some temptation can be a good thing depending on the situation and the context it holds. Opposed to this, I can also say that it is also a good thing to resist temptation; to not give in to what we want when we want it. Most importantly, this references back to the Greek theory of "balance" in life. Does this balance enable us to make these choices? Do we get too carried away with giving in to temptation or resisting it? These questions have to be asked by the individual at question. Only they themselves can judge this for only them.

Good people via fear

"It is hard to believe that even a good man would stop himself from stealing and doing all kinds of other bad things, if he knew he would never get caught."

Fear does keep people in check, but that makes society sound scary. It's not so much fear as the norm. It is the norm to obey the laws and do everything you can to stay clean, which puts doing bad things out of your mind. It's just not relevant enough to think about doing.
Add an invisibility ring to this equation and you would, of course, start small. Maybe steal your Tim's coffee if you didn't have the change and were in a hurry. Minor inconveniences would be resolved. And then one day, if you saw someone doing something terrible to the one you love, you may just kill them. But it would take a long time, and, assuming you didn't share the knowledge of the ring with people, "Hey, honey! You won't believe this!" the alienation would be a slow process. But then again, people are more inclined to take personal risks for those they love. People with families can't truly alienate themselves from society.

One, single, lonely man (or woman) with no money, family, and a nasty case of psoriasis would be your likely candidate to turn lethal. I like the "what if" of the origin of evil, because there is no sudden change, it's a slow process that brings circumstances to play that are normally just impossible.