Why is there darkness in humanity?

For there to be a good there has to be a bad. Darkness is a type of bad that supports it in different ways. There will always be people or things that contradict one another. All day everyday can't be light outside and there not everyone is a happy person. There are people that are always going to be against what other people think. It's just the way life is. If everybody agreed on the same things life wouldn't be exciting. The world would be too plain. Some people believe that darkness is a bad thing but there are others that live in darkness and fear light. Darkness is what makes some people the way they are. In some cases people can't help staying in darkness, they think the sun/light is evil. Darkness is in humanity because it's a way of life. Things wouldn't work out the way they do if there was no such thing as darkness.