Here’s another bit of nerdiness for you. Skip it if the psychology of little plastic posthumans isn’t your thing. (Originally posted on my semi-defunct Tumblr some time ago.)
One of the assumptions that occurs in the Warhammer 40,000 Imperium is that everyone who turns away from the Emperor’s Light automatically falls to Chaos. This is at least partially because the wargame tends to divide human factions down the middle: Imperial and Chaos. If you want little human soldiers on your tabletop, they’re waving banners with the double-headed eagle or the eight-pointed star.
As ever, the setting’s deeper than that. There are many places that an Imperial citizen can go if they don’t want to be a part of Imperial society: Canonically, you’ve got mentions of your xenos-loving Tau sympathisers, you’ve got the various rebel enclaves that exist (even if just until the Imperium gets around to stamping on them) and you’ve got human empires that exist outside the Imperium’s borders, either due to a collapse of Imperial rule in a given area, or because the Imperium’s expansion since the Age of Strife has never actually reached them.
And then there’s Imperial society itself. You don’t have to be a loyal Imperial citizen to live in the Imperium. You don’t have to believe in the divinity of the God-Emperor of Mankind. You’ve just got to look like you do. So long as no one twigs that you don’t give a damn about a dead guy on Terra, and you go to chapel just enough that the preacher doesn’t get suspicious, you can exist as a quiet atheist for your entire life. (c.f. Christianity, heresy, and the casual nature of belief in many areas of medieval Europe, which is, of course, the analogue upon which the Imperium is built.)
Ever wondered where the mercenaries hired by the bad guys to kill an Inquisitor or an Abitrator or other representative of the Emperor come from in a theocratic setting? These are examples of Imperial citizens who don’t actually believe in the God-Emperor, or at least don’t associate it with the Imperial regime in the way that any ‘true’ Imperial citizen would do.
In short, humans are capable of not worshiping the Emperor without automatically embracing the Dark Gods.
Space Marines, though, they’re a different kettle of fish entirely. I think it’s supported in canon, although I can’t remember where it was written, if it is, but they have an inherent vulnerability to Chaos.
But the Adeptus Astartes are the paragons of humanity, the strongest in body and mind, right?
Religious conversion tends to come along when everything in your life is falling apart. It’s a way of coping with trauma without going completely insane. This applies to Space Marines as well as it does you or I.
Humans can lose everything, but pick up the pieces and carry on. As already described, they can lose their faith in the Emperor quietly, without it ever affecting the rest of their lifestyle or sense of identity, and without feeling the need to turn to the Dark Gods. Astartes, though, are as inhuman in their minds as they are in their bodies.
They’re programmed from childhood through indoctrination and hypnosis to be obedient, to think of their Chapter, their primarch, their commanders and the Emperor above all other concerns. These are the anchors that hold Space Marines in loyalty to the Imperium.
When a Marine leaves his Chapter, for whatever reason, three of those four anchors are cut free. Only his love for the Emperor is left.
So long as that remains intact, I’d suggest that the renegade Space Marine will stay loyal to Imperial ideals, even if not to the Imperium itself. He will set himself up as a guardian for a remote colony, or set off on a combat-pilgrimage through a wartorn area, or hook up with the Inquisition or another Imperial body, or set himself a specific quest to fulfill his need to serve the Emperor without the usual chain of command to command him and support his emotional needs. (Yes, Marines have emotional needs, just like normal humans. They just tend to be a bit more combat-oriented than the average homo sapiens.) Potentially, entire Space Marine formations could go down this route without ever succumbing to the lure of Chaos. This is supported in canon in at least a couple of Black Library novels.
Most Space Marines don’t worship the Emperor as a god, possibly because their doctrines date back to the time of the atheistic Legions. If a Marine becomes disillusioned with the Imperium, he can blame the petty mortals that have corrupted it from the Emperor’s vision of the Great Crusade, and his loyalty to the Emperor remains intact and all is well and good.
Alternatively, he can blame the Emperor himself and decide that the Man In The Shiny Chair isn’t worthy of his loyalty. Similarly, if the Space Marine is from one of those Chapters that worships the Emperor with a religious devotion, there’s always the chance that, in the face of losing everything else in his life, he will also lose his faith.
Either way, that’s the fourth anchor gone. The Space Marine’s psychology drifts out of its safe harbour and into a storm.
However it happens, with that fourth anchor cut loose, the renegade Space Marine has nothing holding him to his old life within his Chapter. All of a sudden, there’s an emptiness within him that has never been there before. This is an emotional and psychological crisis that a Space Marine should never have to experience, and has no training or experience in how to cope; this is way beyond the scope of any doubts he may have expressed to his chaplains before his exile.
He needs a new anchor, something to keep his sanity in check. Something powerful, something that commands loyalty. Chaos is the most obvious one of those. He’s been trained from recruitment to hate Chaos, to revile the traitor and the heretic as being unworthy of life, and to fear the power that Chaos has over the weak-minded. However, the context of all this hatred is the binary opposition between the goodness of the Emperor and the evil of Chaos. The Emperor’s purity has already been violated in the renegade’s eyes, so how, in that case, can the renegade Marine continue to hate Chaos to quite the same degree as he once did?
It probably won’t happen overnight, it may take a hundred years or more, but that emptiness in the Space Marine’s soul needs filling somehow, and the Dark Gods are always out there, ready to accept his allegiance. His hatred fades to the point where Chaos simply doesn’t seem like the worst option.
And, the joy of this (from the point of view of a Chaos follower) is that it’s not the inherent weakness of humanity that turns Space Marines to Chaos. It’s the Imperium. The Imperium put this need for service and obedience into the Space Marine, and it’s that factor that leads to renegades falling to the dark side.
As is so often the case in Warhammer 40,000, the Imperium is a tragedy. It is its own obsessive need to keep the Astartes under control that spawns new enemies.