The Cultists are a contradiction. Much like the Gaians, they value not disturbing the native ecological processes of Planet. Unlike the Gaians, however, they do not value humanity having a presence on Planet. They revere Planet with fanatical devotion – the name ‘Cultists’ is more description than slur – and believe their leader to be born of Planet. While there are many who are born on Planet, there is only one person born of Planet, and his goal is to undo humanity. To quote the description of one of the civilizations in the Civ 4 mod Fall from Heaven 2: “some believe they will receive an eternal reward for destroying creation, while a few just want the world to end”.
The contradiction lies in that to succeed in the goal of cleansing humanity from this new paradise, the Cultists will have to go on being very much a human presence. They will have to build bases, factories, units – and lots of them. It is one thing to be a conscientious objector to the traditions of indiscriminate ecological ravaging inherited from Earth; it is quite another to mobilize meaningful resistance to their implementation by the other factions. The other factions are unlikely to stop their survival efforts simply because they are asked nicely to do it, and the only way to ensure success is to bury their cold dead bodies under a patch of xenofungus. For that, you need guns. Lots and lots of guns. And shovels.
For this reason alone, every Cultist attempt to achieve their stated goal is simultaneously a step away from actually succeeding. While it is necessary from a tactical and strategic point of view to expand production, grow the population and dot the landscape with ever more infrastructure, these very things are explicitly against the ultimate aim of the faction as a whole. It is a cognitive dissonance of the highest order, and it is probably not a far reach to assume that this is a contributing factor to the Cult of Planet being a, well, cult.
Another layer to this is that even if the Cultists were to succeed in convincing members of other factions that humanity is a blight on Planet, this would only accomplish a general malaise rather than radical societal change. Much like extreme radical environmentalists are utterly marginalized on the Earth we know, so too would they be on Planet; the ruthless inertia of status quo keeping at it would ensure that the pollution practices continued. The result would be an alienated despair at the state of things – another inherited tradition from Earth.
Nevertheless, for all these contradictions, the Cultists do possess the theoretical means to achieve their goal with swift efficiency. Mechanically, this takes the form of a high innate chance of capturing Mind Worms. These Mind Worms can then be let loose upon the world to capture more of their kind, essentially snowballing the process until the Cultists control sufficient raw biomass to simply overrun all other factions. This approach runs into the same cognitive dissonance as utilizing a more gun-based route (domesticating the natives is fundamentally the opposite of letting them roam free as nature intended), but here too the end will justify the means. As to these ends, ponder the leader quote:
Mankind has been blind for thousands of years – for all of its history. We have come to a place whose wonders are a hundred-fold more amazing than anything on Earth. Around us is clear evidence of the will of a higher power. I bring the Vision to the blind eyes of men. I bring the Word to the deaf ears of men. I will make them see it. I will make them hear it.
– Prophet Cha Dawn, “Planet Rising”
In terms of religiosity, this is a far cry from Miriam’s more considered stance on the place of humanity in the grand scheme of things. Where the Believers hold Planet in disdain for being alien, the Cultists hold humanity in contempt for pretty much the same reason. A casual glance would suggest that this implies an affinity towards the alien factions, given their shared view of humanity. However, the Usurpers seek to coopt Planet for their own ends, which is very much not in line with restoring Planet to its pristine state. Ironically, the Caretakers agree whole-heartedly with the Cultist assessment that humanity has to be removed from Planet, and see no compunction to beginning with the Cultists themselves.
This leaves us with the question of whether or not the Cultists would lead humanity into transcendence. If successful with their original aim, there would not be a humanity left to transcend. If unsuccessful, it would more likely be the result of a metaphysical arms race than anything else; as the Cultists become ever more post-human, the aim shifts from physically removing the other factions to beating them to the punch. By being the first to transcend, the Cultists can use their newfound godlike capabilities to downsize the human presence on Planet, or remove it altogether. This back-pedaling into victory would be the logical conclusion of the contradiction inherent in the Cultist faction. In order to prevent humanity from irrevocably changing Planet forever, they would have to be the ones to make it happen. Even ultimate victory would be self-defeating.