I have difficulty viewing it as an element. Darkness itself does not give light its structure, thought he contrast certainly helps give one an appreciation of light. Light, or rather the absence of light, gives birth to darkness. Light gives birth to all things, really, as without it - the massive explosions at the heart of creation, from the formation of solar systems to the Big Bang - nothing could form. Without light, there is simply nothing. And so there we have darkness.
Do we then call the absence of existence an element? Or simply a vacuum looking to be filled? I do not see how it pushes things forward. I do not see how it has anything to do with death, demons, or anything of this nature. Darkness simply is simply empty. *shrug*
In more esoteric points of view, we might examine this nothingness as an aspect of lower spirits and entities, incapable of feeling higher emotion or formulating deeper though, and in turn generally feed on the lower emotions, negativity, and attempt in jealousy and anger to mimic or feel that which might be greater. But still, I find little to learn from this beyond an appreciation for that which we are given in light, and a sorrow for those who know its lack.