Well just because you don't believe in sin does not prove there is none. Why should I believe that?
Evil is everything unholy or pure which is obviously everywhere in this world as we know it. We fall short of Gods standard all the time in this world, he did not intend it to become this way but he knew it would when Adam and Eve disobeyed. I do get upset because after that everyone was doomed but Jesus made a way and that is good news.
I define evil as to what the Bible says is evil. Start with the 10 Commandments first, then in the New Testament defines what the deeds of the flesh are verses the deeds of the spirit... Gal. 5:19-21 The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.