Well, I've been thinking a bit about Chaos. I don't like how it has been presented in the fluff as it's been presented recently. I know GW have tried to turn it round a bit, but it's still basically "Chaos is evil, Chaotics are evil, purge the unclean" stuff.
So.. what I think is..
Chaos is, generally speaking, the manifestation of the intangible. Emotions, thoughts, etc. Collectively, Chaos is the Warp. Chaos is within everything that experiences emotions, whether they be fear, love, hatred, agony or whatever.
Everyone, from the lowliest Guardsman to the mightiest of Space Marines, is inherently suffused with Chaos energy. It is the basis of life and cannot be denied. Without Chaos, there would be perfect order - no emotions, no feelings, no hatred, no passion, just existence.
Then we have the 4 major Chaos Gods, the roughly divided personifications of these collected energies (though there are many places where they overlap, and many smaller entities that come and go as certain emotions become particularly strong). Note that I consider Chaos Undivided to be the total of all these entities, rather than a specific entity itself.
Below those, we have Greater and Lesser Daemons. Although we only see combat daemons, I consider Daemons to be smaller, more localised manifestations of these energies and thus there would be daemons interested not in ripping people limb from limb, but also helpful daemons like Faeries, Djinn, creatures to lead lost travellers back home, etc. We don't hear about these in the fluff for the same reason we don't hear about Eldar prostitutes - they have no place on the battlefield, which is what 99% of the fluff talks about.
So, what happens when someone "falls" to Chaos? Well, they don't actually fall to Chaos. Chaos is the instrument of their destruction, but the path was their own creation. Chaos contains great power, and the lure of power inevitably attracts the greedy, the craven and the tyrannic. The whisper of daemons is that of our own thoughts given shape in the Warp, compelling us and offering the power of Chaos which the evil then craft into their own designs.
In short, those the Imperium think are "tainted" by Chaos are merely the evil people who use Chaos as an instrument. The blessings of Dark gods occur when the energies from certain emotions are so strong that they manifest in this material plane. Daemonhood occurs when an individual becomes so enveloped in Chaos that he transcends reality to become Chaos, a collection of emotions and thoughts strong enough to maintain a shape in the material plane.
This is not just something that occurs for the evil. Saints are those who experience exactly the same thing as a Daemon Prince, except from experiencing different emotions and therefore becoming a different type of daemon, but the principle is the same.
The Imperium fears Chaos. Though every last one of its living subjects is inherently Chaotic, they all have the fallacy of man, to try to gain power, to abuse others. It is those whose ambition is strong enough to make them aware of the Chaos within them that pose the threat, and when such ambition is married to the increased Chaos energy they embrace they become even more dangerous. Yet many use Chaos without knowing it, their very ignorance a shield against corruption and the evil within them.
It is therefore possible to embrace Chaos without harm if one's intentions are right. However, due to the nature of humans, this is almost impossible to do consciously without being overcome by the lust for power. There are still many, many examples of this happening - people in desperate situations suddenly endowed with power they never had, not knowing that they had temporarily become a conduit for the Warp.
Anyway, I'm not really sure what the point of all that was, and I have no idea how much of it is contradictory to existing fluff. Either way, I thought I'd type it up and throw it to the fluff sharks out there.. hmm, fluff sharks.. what a disturbing thought. Discuss!