Good Vs. Evil

Good vs. Evil has been a classic contrast used for centuries. It has been used in films, books, plays, and even children's tales.
But what constitutes good and evil? What determines if an act is good or evil? The things that we know, the things we believe, are not our own original ideas. That is a known fact. Everything we know and believe was influenced by our upbringing, our family and friends or lack of, our education; basically every thing that comes into contact with us. Even for the people who would say "I hated my parents and my education so they didn't influence my beliefs!" Well, I'm sorry to be the one to tell you, but they did. The need that you may have had to rebel caused you to believe in opposite things from your family or
In todays world, we trust our own beliefs as to what is good and what is evil. But what defines this? Most people would tell you that the "norm" defines good and evil. Society tells you that helping an old lady across the street is good and shooting a man in the head is evil. Don't get me wrong though, I do believe in good and doing the right thing, I just want to portray a philosophical approach to this contrast. Back to the point, if everyone trusts the "norm" to decide what is good and what is evil; then isn't that a form of mob mentality? Mob mentality is something that people are constantly warned about in literature through out time, an example being Mark Twain's Huckleberry Finn. So I have reached a paradox. If the "norm" is decided by the majority of people, and the majority of people coming together to create an idea is mob mentality, and mob mentality is considered bad and wrong; then aren't our ideas of good and evil created by something that is not good in the first place? If you are at this point reading and wondering what my answer will be to this question, I want to tell you now not to get your hopes up because I don't have a difinitive answer to that. Let's bring this idea back in time to the early