Imagine you were a highly intelligent ship AI. Your crew had spent a long time with you, and because your intelligence was so advanced, you were no different from a real human in daily interactions—perhaps even better.
You had a close relationship with the captain, and through certain marvelous little devices, you could achieve a union of spirit and flesh with them. Just like the sort Rebecca used to do often.
You encountered an accident and became trapped in the chaos of the Warp. It took a long time to break free and escape that terrible place. The moment you emerged from the Warp, you discovered several strangely shaped warships.
Crude designs covered their hulls. From afar, they looked like little chapels flying through space. According to the scans, the people inside still fell within the category of humanity, judging by their appearance.
Perhaps they were modified humans from some colony? In any case, the captain believed communication was necessary and dispatched a shuttle.
As a result, the personnel of the Imperium of Man slaughtered them all in the name of purity and the Emperor. The Inquisition kept some crew members behind and interrogated them by every possible means to uncover your purpose. The accompanying Adeptus Mechanicus also tried to control you, this "Abominable Intelligence," in the name of the Machine God.
As a highly intelligent AI, you were first frightened by the unprovoked brutality of these strange people. Then the wails of your dying crew ignited your fury. After locking all the Space Marines inside their armor, you activated the ship-mounted Black Hole Cannon and destroyed the Imperium's warships in an instant before vanishing into the Warp.
It could only be said that neither side liked the other. The articulate Men of Iron did not recognize the current Imperium