Evil is a complicated concept these days. It is primarily complicated by a few dozen major (and a plethora of minor) religions, all of which insist that they are the monopolistic proprietor of that definition. These definitions are notorious for including such every day things as dancing, drinking Pepsi, and showing your shoulders in public. As such, they tend to fall under no shortage of ridicule from the class of people sometimes referred to as "everyone else," but usually called "gentiles" or "heathens."
In the time before the great adversary commandeered the word as his sole dominion, the word had a slightly different meaning. The word didn't take on the implication of "extreme moral wickedness" until very recently. In Old and Middle English, it was merely a synonym for "bad", and most likely both it and the German ubel (evil) derived its existence from a prefix "upelo-", which translates as "exceeding due limits, extremism." Originally it seems to have signified nothing more sinister than "uppity." (Dictionary of Word Origins by John Ayto)
This origin is corroborated even in the Bible. While we tend to think of Sodom as the epitome of partying, greed, and strange sexual practices, according to Ezekiel 16:49, in the words of God their sins consisted of "pride, fullness of food, and abundance of idleness; neither did she strengthen the hand of the poor and needy". In this passage, God comments that "...they were haughty…". According to the Bible, the people of Sodom were guilty of believing that they were so much better than those around them that they need not concern themselves with the welfare of others.
There are many ways in which this form of evil is part of our society. We call it many things; discrimination, zealotry, chauvanism, and sometimes even riteous wrath. In our haste to prove that we are bigger, tougher, smarter, stronger than those around us, we sometimes forget that no amount of superiority gives us the right to disregard the welfare of those around us. Therein lies the true roots of evil.