Related:

• Reason as memetic immune disorder "The reason I bring this up is that intelligent people sometimes do things more stupid than stupid people are capable of."
• Nerds are nuts "I was not surprised that the RSS had a core cadre of scientifically oriented leaders. This is a common tendency amongst faux reactionary movements with a religious element."
• Compartmentalization (from the wiki)
• Epistemic learned helplessness - "He told me a good portion of the point of CfAR was to either find or create people who would believe something after it had been proven to them. And I nodded my head, because it sounded reasonable enough, and it wasn't until a few hours later that I thought about it again and went 'Wait, no, that would be the worst idea ever."

tl;dr brains don't have virus checkers; compartmentalization and difficulty in being convinced as memetic immune system.