How fun, mine is, as well, and on stuff like the Garro books and a bunch of other HH and regular 40k, including Eisenhorn, Necromunda, the Fabius Bile novels, the Ahriman series and Sandy Mitchell's inquisition books.
And I welcome any evidence from there that supports your position. Namely that it is the desire to excel or having emotions alone that matters in regard to Chaos and not "rogue psykers,aliens and other Chaotically-influenced entities" that caused people to fall to Chaos.
They do so because of the actual structure of the Imperium
Needless to say I don't share your optimism concerning the Inquisition and other citied organizations. In particular their ability to maintain a meaningfully watch over any significant fraction of the Imperium population. If anything they are depicted closer to firefighters constantly putting out blazes that have long festered rather than actively preventing heresy and corruption taking root.
A case in point, if we shift to Ordo Xeno, is in Sandy Mitchell's "For the Emperor" we have a Genestealer cult which has infested its way all the way up through the leadership of the planet Gravalax up to and including the Planetary Governor being a hybrid complete with an obvious mutation of a third Genestealer like appendage.
So I don't see any evidence the upper classes are particularly resistance to corruption or Cults. Certainly societal pressure is insufficient especially with how much power is invested in the hands of the elites versus the rest of society.
Doesn't that disagree with your previous assertion Chaos is fueled and concerned with only emotions and desires to excel? Because that very much sounds like Chaos as I described it. As something requires an outside factor to cause corruption. To be sought out or insidiously brought in by others.very good reason why "An open mind is like a fortress with its gates unbarred and unguarded" is part of a litany, because the liberal and the openminded planets of the Dark Age of Technology were overrun by rogue psykers,aliens and other Chaotically-influenced entities.
Additionally ignorance does not protect you from Chaos as the Horus Heresy very well established. So keeping your mind closed is only going to cost you in the long-run. Again the Federation viewing them as just another set of omnipotent aliens is likely going to pay massive dividends long-term both in educating their people of the threat Chaos poses, similar to the Interex, and studying ways to combat and reverse its influence.
Considering how long DAoT lasted, the heights they achieved, I don't think being like them is an all together bad thing. The Imperium can only exist because of the former's legacy after all. Further the Federation is a well-maintained, moral society not given to excess or indulgence with citizens that are happy and content. That's as far from a perfect breeding ground for Chaos as you can conceive of. Certainly they will have to become aware of Chaos and monitor for it but that is a doable endeavor.You do not understand Chaos, and the Federation is the perfect breeding ground for it, with its innate weaknesses that are reminiscent of Humanity during the DAoT, their peacenick and anti-theist and pinko commie tendencies make them even an easier target.
I will point out that it is unclear, at least to my knowledge, if the Federation can be claimed to be anti-thiest. I don't think they preclude or discourage worship. Certainly Worf was never chastised for his religious beliefs. In the episode "Bread of Circus" Christianity was giving a very positive view while in "Who Mourns for Adonais" Kirk rejects Apollo worship of him saying humanity found " the one quite adequate".
They simply are used to aliens pulling off God guises or have God-like powers even if they don't claim to be divine ala the Q. So Chaos isn't anything that new to them in that regard even if it is a lot nastier than they are accustomed too.