Dumbrella

a psychological defence mechanism to deflect and repel droplets of facts that could threaten your world view, for example someone in a cult who refuses to listen to facts that would be difficult to reconcile with the teachings of the cult. A person deploying this device attempts to remain uninformed ("dumb"), having deluded themselves into believing the shower of facts raining down upon them requires protection, as if sheltering under an umbrella.

When I tried to show him one such contradiction in the cult's own literature, he deployed his dumbrella, sticking his fingers in his ears and walking away.