A LOT OF CONCEPTS TO COME.
Darkness is the force of corruption, chaos, and freedom. Most denizens of the internet have a mix of Light and Dark elements. Light is not necessarily good, just as Darkness isn't necessarily bad. Without Light, life would descend into chaos, and progress would come to a halt, as there would be no well defined system or infastructure to build upon.
The Lightcrest absorbs Light from the surrounding environment, leaving Darkness in its place. Those who've had ALL of their Light drained become criminally selfish and wild, doing whatever they want, including killing others.
Boozerman had most of his Darkness drained, however the effect was lessened by the alcohol in his system. There, problem solved.
Light prevents the negative aspects of Darkness, and vice-versa.
Darkness additionally has the attributes of persistence, indirectness, silence, emotion, determination, fluidity, cold, and obfuscation.
See Study:Light And Darkness for more information.