First off, one must understand the cosmology of the dominant civilizations in a place to begin properly understanding that place. The Negaverse was shaped by one key event of our own prehistory. It was "discovered" by accident during the last in the series of Kellek's many attempts to return to his own time in defiance of his banishment by Roah and the other Forerunners. Rushed gate construction meant that many of Kellek's revenge gates possess Niode matrices that have idiosyncrasies. This was desired for anachronous warping but is derided by Drochah oh-Thyehgr as a quite sloppy method of time travel much less elegant than his own temporal manipulations. That commentary aside, what would be Kellek's final resting place was a parallel universe nearby ours. You see, he didn't succeed, chronologically speaking. The time period Kellek jumped to was still chronologically locked at our prehistory and the Negaverse's Norunners at this point were still at the very early stages of guiding the evolution of their servitor races. The more primitive Nobearer civilization was heavily influenced by Kellek and impressed by the slapped together technologies he possessed which though not as advanced as those of Roah and the others back in our own time window were still a good deal more sophisticated than what the Norunners had access to prior to his arrival.
The Norunners began worshiping Kellek as a god, and the screwed up values they developed were in line with those of the mad warlord. These are: 1.) Domination of one's environment is good. This allows you to maximally exploit the life forms and natural resources to your fullest capacity. 2.) Disregard for the consequences of one's actions is fine as long as it gets you what you want. Forcibly alter the atmosphere of a planet or irrevocably change the natural course of evolution for a population of lower/lesser life forms? As long as you can still use it to your advantage, not a problem! 3.) Development of cabals allows you to outnumber your enemies right in front of their noses.
Unbeknownst to the Norunners this was a strategy Kellek implemented to keep them divided, allowing him to quickly and permanently establish himself at the top of their hierarchy... by eliminating any but those who were unified in their support of him. Though not the exact revenge he had wanted, taking things out on the Negaverse did allow Kellek to achieve a form of it. He wound up crafting an entire dimension's Forerunners into his own servitor race!
Anyway, after he died the Norunners (whom he had also deemed to be a lesser species than himself and done a series of experiments on) wanted to maintain their status quo and felt the best way to do this was through emulating Kellek. They adapted his brutal methods to their subjugation of the Negaverse.
Cybernetic grafting, horrific induced mutations, surgical alterations and other extreme techniques which they saw their terrifying god-king and pharaoh use to terrific effect in his armies on his soldiers and on themselves inspired the Nobearers to go out and craft their own servitor races in a similar fashion, while continuing to modify themselves. They felt these transmogrifications were "self-improvement" and this distinct paradigm shift after Kellek (that the transformations are not simply a tool but in and of themselves a desired state) carried on all the way down into many of the Norunners own creations. You'll find it as a recurring central motif in the major religions of Antihuman society to this day.
I say many of their creations because there are a few notable exceptions.
One opposition Norunner, though still about as horrible as the rest realized that strict adherence to Kellek's laws would not be sustainable to Norunner civilization as he observed Antihuman societies start developing. So he created the Ratmen as a race of cleaner uppers to deal with the pollution and other problems generated by the wasteful Antihumans. He instilled them with a somewhat modified set of Nobearer values, so the Ratmen would view recycling as the highest form of resource exploitation and scavenging the ideal way to dominate ones' environment. I say equally as horrible because he shared the cruelty of his other Norunners. Before he could finish breeding them for obedience some escaped into the wild. The Ratmen are loath to transmogrification and the more holistic culture of their civilization allows them to dwell within and underneath that of the Antihumans. These two groups, the Antihumans and Ratmen exist adjacent to each other if not in complete symbiosis then at least commensally for the most part, although occasional conflicts between the two are not unheard of.
Antihumans, to psychologically cope with their nasty way of life took to their cults of transformation with upper echelons of clergy in these often articulating the typical commonly held erroneous delusion that they are the direct descendents of Norunners (instead of simply their discarded playthings) in their teachings. Transmogrification societies dedicated to this dark "self-improvement" dot the Antihuman cultural landscape. However, among the more urbane and erudite of these, it is generally acknowledged that the Norunners were both great and terrible, tremendously selfish powerful beings, who lacking scruples, would oft swoop down on worlds, bringing a host of pestilence, famine and mutations.
These religions tend to take two forms:
Moderates: Unlike their original Norunner creators, these Antihumans believe it should be one's choice what "improvements" to receive. Take charge of your own destiny by directing your own literal transformation (to what extent you can!). Transmogrification is to be done for reasons that are the personal, as a means of surviving to extend one's life in spite of ailing health or sterility, make doing certain tasks easier, etc. This self-improvement is celebrated in contemporary Antihuman society. Praise Kellek!
Hardliners: There are rumors of fanatic sects attempting to gather what technology and dark secrets they can to resurrect or revive the preserved remains of their demonic Norunner "gods", as a general backlash to the more moderate form of transformation occultism gaining popularity... something they regard as infectious blasphemy committed by heretics. Who are we to act outside the interests of our betters who came before us? We must keep things as they were. To return things to how they "should be". In order to keep carrying out the Norunner legacy (and by extension Kellek's revenge). it must be in the way which they had intended!
Submitted by Mycobacter#712744