Evil can only come from conscious thought that destroys the common bounds of culture for the sake of self-gain.
Not really a theory; it's pretty obtuse. What I meant to say is that what is usually defined as evil comes from someone who has taken a "shortcut," as it were, through what is acceptable to a civilized group of people with standards. Like killing your opponent in a footrace. Hacking the school computer to raise your grades instead of passing tests. And so on. But then there arises the fact that evil is more of a strong statement than "wrong." In the two examples I gave, most people would call the first one evil, and the second one "wrong." Unless you lost the "Best Student cup" to the guy who did this, then you'd probably take it more personally. Which is another "gray area:"
Evil is about perception.
You may ask, "Uh... Punkie? Things okay at home?" Yes they are, but I had a great IM session with someone today about it, and this is also part of my writing because my protagonist has to have a more sharply defined sense of "evil" because... well, it is fiction, but I want it to be at least plausible.
The basic tenet of most evil is usually defined as destruction, like the asshats who crashed into the Twin Towers on September 11th, 2001. Hurricane Katrina was FAR more destructive, but it's "not evil" to me because it doesn't have a conscious mind to realize its actions. But both ended in people using the disaster towards their own gains, from the "accepted benefits" of people who become heroes, jobs created for rebuilding, new houses being built where the old ones were in bad shape anyway but not bad enough to warrant knocking them down... to the "unaccepted benefits," like people looting, killing off people they didn't like because they know there's little chance of it being blamed on them, and the politicians who use the image to glorify themselves and get elected, only to declare wars on countries with no real good reason. Destruction begets creation, too. Look at Hawaii. Volcanoes are VERY destructive, but generate new land so life can flourish. The US Revolution killed a lot of people, but ended up as a fairly (until recently) benign superpower that fostered some of the best inventions mankind has ever seen.
So evil vs. good is not so easy to define.
What sayeth the peanut gallery?