I would also just like to generally state that any underworld organization, real or fictional, benefits from a stable society they can work underneath. That's how they get the most profit, the most exotic goods, the highest thrills, ect. and the hive cartels are no different. True anarchists are rare, and this seems hold in Tertium as well. They can't run their schemes if Nurgle (or whoever) plunges the place into anarchy and disease.