Without that belief, without Jesus, the penalty for sin and not loving God remains the same. Everyone who does evil hates the light, and will not come into the light for fear that his deeds will be exposed. You see, mankind still hates Jesus. Jesus is the Light that exposes the evil in the world. Nobody likes to admit they are wrong.
Nobody wants to think they are a bad person.
That is called Pride and Selfishness. It's another way of saying that you are more important that God. However, pretending there is no such thing as sin is like pretending you won't fall if you step off of a cliff. It's still there. It's still true.