In a dysfunctional age of darkness and decay, a careless word is enough to land you in hell.
Most Low Gothic dialects across the Imperium of Man sport a double meaning attached to the word for 'whisper', and indeed a great many dialects sport two different words for the act of whispering: One denoting whispering in order to avoid detection, and one denoting whispering to inform on others.
It has been thus for millennia upon millennia, for rulers who live in fear are the most dangerous of all. In the Age of Imperium there is no shortage of insidious horrors to keep the Adeptus Terra and its host of Planetary Governors on edge, dreading what lurks in hiding. A myriad of ambitious plots are everyday pursued by Imperial nobles and bureaucrats, some aiming at coups and assassinations in the bewildering world of human games of power. Shady nests of insurgents and cultist cells feed off widespread discontent to further their plans of sabotage and uprising, ever threatening Imperial rule with the heretical scourges of separatism, revolt, apostasy and abominable blasphemy. To speak nothing of the ever-present threat of invasion from beyond the dark void, some attacks of which do not unite beleaguered worlds against an external foe, but on the contrary lay bare internal divisions as rival sides seek to turn the uncertain new situation to their advantage in a confused frenzy of broken alliances and civil war.
With so many deadly perils hanging over the head of the masters of mankind like the sword of Damocles, how could Imperial Adepta and local rulers do aught else than clamp down with harshness on the populace, for their own good? With the preservation of Imperial law and power under danger, how could the servants of the God-Emperor dare to do anything less than uphold a rigid order of terror which tolerates no one speaking out of line? With the survival of the human species itself at stake, how could virtuous subjects of Him on Terra fail to report suspicious talk and deviant behaviour to the righteous authorities?
After all, those who fail to police their community with vigilance and cunning, will damn it to oblivion. To not report, is to partake in the treachery. There could be no worse crime than allowing the slightest hint of hidden heresy and thought of self to escape detection by the guardians of humanity. Aid our watchmen: Keep watch! Those loyal to their species and lord will know to listen well to all people around them, and discreetly inform on any suspects to the Adeptus Arbites, Inquisitorial agents or local law enforcement and counter-espionage networks.
To the pious and staunch subjects go the spoils, for the Imperium know well to reward its informants. Indeed, for many slaving people trapped in squalor and grinding poverty, the rewards for ratting out on a neighbour or colleague may be the only way to alleviate their misery by some extra company scrips, coupons, ration bars, tech-trinkets or meager luxuries unusual to your rank, and any number of other perks and bonuses which many downtrodden humans would be willing to kill over. Yet pecuniary gain is not the only material incentive at work. When your crowded family live in each others' laps and shares an apartment, shack or holestead with several other families, the best way to earn some breathing space and bunk room is to denounce members of the other families, and watch as security police makes them disappear, never to be heard of again. As the Lectitio Divinitatus states, the righteous will oft be rewarded in this life as well as in the next.
And so humanity under the heavy rule of the Imperium watch each other and whisper on each other. The Imperial culture of imputation has ensnared society in a web of distrust and deceit, and sown suspicion everywhere. Strong ties to your clan or tribe is no guarantee of safety, for greedy, spiteful or loyalist informers can be found everywhere. Who have not heard the glorious tales of good children who reported their own mischievous parents to the authorities, and died the glorious martyr's death as their vengeful extended family murdered and tore them apart? Who have not listened to the uplifting songs praising such youthful duty? Who have not seen the posters, statues, pict-casts, theatrical performances and holo-dramas hailing such young virtue and loyalty to His Divine Majesty?
Thus the spider's web of informants every day, somewhere across the Emperor's vast domains in the Milky Way Galaxy, repeat that baleful tragedy over and over: That of sons and daughters denouncing their fathers and mothers, or their sisters and brothers or other kinsfolk. That of children betraying their own parents to the authorities for the sake of grumbling words against cruel overseers after a taxing shift, or for the sake of more guilty scheming. That tragedy of people who died in the torturer's chambers, labour camps or on executioner's squares because their own offspring or siblings informed on them. That of Imperial loyalty trumping filial piety. That of families torn apart.
For no tyrant ever had trouble finding willing henchmen to carry out their heinous bidding, and no despot ever found a dearth of humans willing to sell out their friends and loved ones.
Much of our species in the far future ekes out a miserable living to a constant background din of paranoia and squealing, an everyday mistrust of fellow man that is frequently drummed up to a crescendo of arrests, torture and a domino effect of panicked denunciations as yet another wave of terror and purges roll out across hundreds of thousands of Imperial worlds and uncounted voidholms. The rhythm of such campaigns of repression varies wildly, often being dependant on the commonly depraved character of rulers and their moodswings, or on crisis events and disasters leading to angered calls for culling the disloyal among the populace.
And why should such waves of terror ever be uncalled for? Clearly, each one catches many infidels and traitors in its claws, and each purge manages to force most of these foul heretics and recidivists to confess and name yet more sinners participating in their undermining schemes, for how could their craven souls resist the noble art and purifying tools of torture? The bountiful harvests of uncovered snakes, who name yet more backstabbers, plotters and terrorists in a vain attempt to save their worthless skin, is a healthy sign of Imperial justice at work. The mass graves and pyramids of skulls generated by the Imperial terror waves are monuments to the cleansing redemption of mankind itself. Witness the forces of order lead off the wretched deviants and malcontents to their rightful doom. Listen to the jingling of their chains. Show no compassion or mercy to these wrongdoers and filth. Nay, let them know what you think: Howl at these heretics! Let your hate fill your lungs! Hate!
Thus the Age of Imperium trudges on, as a star-spanning colossus on feet of clay crush both the innocent and guilty with little distinction and no remorse in its heart of stone. For the rotting Imperium of Man will purge any hint of threats from within to its tyrannical rule with fierce bloodthirst and lack of mercy. Its symphony of loud proclamations and staccato of violence is set to a background murmur of distrustful whispers. And so brother reports brother, and sister denounces sister in a neverending cycle of terror.
Such is the depravity that awaits our species. Such are the depths to which humanity will sink.
In the grim darkness of the far future, man must watch his tongue.
And all is well in the astral domains of the ascended Emperor of Holy Terra.
All is as it should be.
Embrace the ultra-grimdark!
40k is meant to draw inspiration from the most depraved aspects of human history. GW has done a good job at worldbuilding, but we can go so much longer and flesh it out in detail, true to the regressed spirit of the setting.
This needs to be the darkest of futures, after all. Nothing less will suffice.
"I gave everything I had to you, to them. Look what they've made of our dream. This bloated, rotting carcass of an empire is driven not by reason and hope but by fear, hate and ignorance. Better that we had all burned in the fires of Horus' ambition than live to see this."
—Roboute Guilliman, primarch of the Ultramarines, 999.M41