Also being one of the, as far as I can tell, more chaos friendly members of our game I'd like to throw my hat into the little debate about the allure of chaos. In all honesty my fav side has always been Chaos on the table top I have a Chaos army and I'm in the process of corrupting my IG army(actually creating a little story around it ;D), and I fully realize that if I were in the 40K vers I'd be on the side of Chaos in some form or another(I also realize I'd probably wind up being a cultist w/my luck). I think that Chaos draws mortal humans in because is because in some ways it's more human than the Imperial Cult. The Chaos Gods didn't come from nowhere, they were birthed(with the exception of Slaanesh) from human emotions and desires. And they all are reflections of the things that lay within every man and woman. Also the Imperial Cult and Chaos are opposites philosophy wise. Besides the obvious order vs disorder. There is also the fact that the Imperial Cult dictates you should sacrifice for others. Where as Chaos in its most basic form dictates that others should sacrifice for you. To me its the whole 'would you rather be the dim bulb that lasts longer or the bright one that dies faster' question and its no surprise that many find the prospect of power, immortality, or at the very least a 'fuller' life more attractive.<br/><br/><br/>As far as the Chaos Marines go its IMHO the story of spurned sons rebelling against their father. If you look at the Primarchs who joined Horus's side they and their legions were the ones who were thought of as scary, brutal, decadent, ect. They were the ones who were sanctioned by the Emperor for being/doing what he had created them to be/do.  From their perspective they were being scorned by their father and his followers for doing what their father requested of them. While other legions were being idolized. So while Horus did provide the spark that started the fire of rebellion, the wood used to create that fire was chopped and stacked by The Emperor, the loyalist legions, and the Imperial citizens. Also I admit there are a few exceptions to this generalization ;)