Why can't they see?

I've wondered from time to time just "how dark is darkness?" How much darker must something (someone) be that we feel the need to add the "ness" to dark. From the front page to the evening news the atrocities still shock! Just how dark is darkness? I shutter to think. In Genesis, God says that "the imaginations of their hearts were evil all the time" I would say that's pretty dark. Why even mention this? It's because we live in the dark, that's why we can't see.