This actually goes hand in hand with the idea that sin does not exist. People are good (edit: I'd like to add here that I don't think that people are inherently evil. People are good. However, after the fall of man we have to deal with sin... the problem I have with the new trendy "spiritual" idea of goodness is the view that everything that people do is good and there is no such thing as sin.). They say that evil is simply a perversion or twisting of some natural good and not actually sin. And there are quite a few ideologies that offer to explain away all that is wrong in the world and mold it fit to their own needs (the socialist and the capitalist would explain all that is wrong in the world using very different words, none of which would involve "sin" as part of the explanation).
Yet this is not the picture of reality that Jesus leaves us with upon reading the Bible. Satan is very much a reality in this world, as is Hell. Peter Kreeft explains it well in How to Win the Culture War:
"Evil is not trivial, and therefore its first inventor cannot be trivial. Satan must be chuckling over the modern media stereotype of himself as a horned clown in a red tutu, or the alternative one- more abstract but just as toothless that sees him as mythic projection of human weaknesses. For no one really fears either a clown or an abstraction.It's ridiculous to mock this sort of evil. Maybe that's why it's become so easy to let monstrous evil just slide by (i.e. the killing of unborn children).... because many people have simply decided not to believe in evil at all.Christ took Satan very seriously (though not obsessively). If we do not, how can we say our minds are on line with the Lord? If we claim to have matured beyond belief in Satan, we claim to have matured beyond Christ. If we scorn the fear of Satan as foolish, we are calling Christ a fool, for he told us to fear him (Matthew 10:28). And if we think of Christ as in any way a fool, we are either denying the Incarnation, denying that Christ is God, or else saying that God is a fool. For if fear of Satan is foolish, and if Christ taught it, and if Christ is God, then God is foolish.Christ commanded us to conclude the only prayer he ever gave us, the model prayer, with "Rescue us from the evil one" (Matthew 6:13). The Greek word is a singular noun, not a plural or a participle, and it has a definite article. The proper translation is not just "evil" but "the evil one.""(emphasis mine)Peter KreeftHow to Win the Culture War pg. 39-40
Just think of all the atrocities that occur when good people do nothing and let evil (which they can hardly believe really exists) simply slide by.