In the Oryx:Defeated grimoire card it says that now we have killed him so we are gods ourselves and emulate him. So... if we are hive gods all the enemies we kill after we kill oryx are technically sacrifices to ourselves. Also in our killing him we have mantled his title of a god and we also destroyed potential gods (Ir Anuk and Ir Halak). Finally if we technically hive gods wouldn't the Hive want to kill us so they can become gods themselves. I have explained the Hive's aggression against us prior to killing Oryx and the other races aggression alongside that.