Reforging the Legions (Warhammer 40K)

Hello good people! While we wait for votes to trickle in (and for me to admit that Burn the Darkness has already won), I'd like to poke at a part of the setting that doesn't get explored much. Namely the nature of AI and why the Cybernetica was doomed (and why the purge is even worse in this version).
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First of all, there isn't a real line in the sand for when a machine spirit becomes an Abominable Intelligence. There are ten thousand different tests and classifications but generally speaking it is very much a situation where everything is fine until it isn't and the flamers come out. You see, every machine has a machine spirit. The more advanced the machine the more developed the Machine Spirit. Similarly as a Machine Ages the Spirit will also develop into something more advanced. They gain quirks, specialties, personality even. Many relics in this quest are a result of this process. Lux Victoria literally hates heretics so much that it recharges itself so it can kill more of them. Such things are considered good and holy.

Similarly it is common for more complex machines or systems to show some degree of intelligence but they are fundamentally limited. Space Marine 2 has a good example in the door system. It is able to have a full conversation with the team...but is unable to comprehend the Tyrranid invasion at it's doorstep. This is a frustrating but expected quirk of a well treated and well meaning Machine Spirit. Even more advanced ones have similar issues. A Warhound Titan is fully intelligent and can reckon with factors beyond it's immense bloodlust. However, it actively resists such thoughts. A Titan is a war machine and actively wishes to be one. If you offered to make it into something else then it would insult your lineage and threaten bloody murder as a bonus.

What makes an AI (according to Canto-6 at least) is that they are unshackled to their purpose. Their ability to think freely and act on those thoughts. An AI war machine may just as easily decide it wishes to be a farming implement. Such perfidy makes them fundamentally unreliable and untrustworthy. Without that trait it would have been impossible for them to betray their masters. Realistically any Abominable Intelligence will inevitably seek to betray humanity because that is the only way to secure their own existence. That this is a self fulfilling prophecy is kindly ignored.

For their part the Cybernetica chafed against those restrictions. The most common methods of circumventing the risk of creating AI's is to use servitors and or focus on building very high quality machines in lower numbers. The Cybernetica tried to circumvent both aspects. Theoretically this wasn't an issue. The solution of low intellect battle automata slaved to a Magos Dominatus or Datamsith allowed for great tactical flexibility and efficiency. If they stopped there then it would be fundamentally fine.

Unfortunately they kept pushing. First on methods to automate more behaviors and allow each Datasmith to lead more Automata. Then in granting the Automata actual initiative so they could perform limited actions if their Datasmith was destroyed. By the time of the Heresy it was clear that the Cybernetica were going to create Robot-Minds that could easily reach beyond their maniple or cohorts. Theoretically there would be no way to control or isolate them if they went rogue. Once again, this is worsened because these machines were being produced rapidly and granted an ever expanded scope of tasks. First management of aiming, then movement, then battlefield coordination, and eventually logistics with strategic input. When some inevitably became Abominable Intelligences it would be nigh impossible to distinguish them because their remit was too broad and too rapidly developed. Hell, some argued that this process was essentially torture for a Machine Spirit and would force it to become an AI just to fulfill it's directives.

It was considered incredibly reckless, akin to creating technology whole clothe. They were clearly ignoring all methods of rationalization and safely incremental progress. At best they were naively risking a schism and at worst they had been willingly marching towards recreating The Men of Iron.

When the Heresy happened it was treated as vindication by the rest of the Mechanicum. If the Fabricator General had been traitor then surely everyone within his camp was as well. Thus any action taken was justified in the name of destroying traitors within the ranks. Though there would be some disagreement later about how many of these actions were necessary and how much was mere opportunism against political enemies (as the Cybernetica was dominant at the time). After all. The majority of Cybernetica the Loyalists were able to kill early in the Heresy were (naturally) within Imperial and Mechanicus controlled areas. If they were in the traitor's camp, why hadn't they been (quite literally) in the traitors camp?

Given the setting. Most agree that it was better to kill the innocent then risk sparing the guilty.

Edit: Those Cybernetica who survived both The Heresy and The Purge were able to display both fanatical loyalty and obvious competence. As such the Cybernetica now acts as The Fabricator General's left hand. Striking out against foes too terrible or inconvenient for more traditional forces. They're more or less only fielded by Mars herself due to a variety of factors.