Board Thread:Warhammer 40k General Discussion/@comment-14745711-20140911102114/@comment-6078851-20140918133950

in short neithan sums it up fairly nicely, every act associated with a god feeds a god - so anything in the galaxy that schemes feeds tzeentch, everything that conciously causes bloodshed and death feeds khorne (that includes necrons and tyranids: "khorne cares not from where the blood flows, only that it flows" so despite them having no direct affect on the warp their actions of killing still feed khorne). and you're very naeve if you think that without humanity no other species will get ill or feel despair and feed nurgle - nurgle was born long before humans even existed. and as for slaanesh, the eldar are simply his/her most potent source, but every sensation of selfish joy from any sentient species feeds slaanesh.

the gods may not want to exterminate humanity but that's only because they are selfish, self serving, and greedy. but the point remains that they don't need humanity. to think otherwise shows a lack of understanding about chaos, or a belief that humanity is more instrumental than they actually are.