I've observed this same issue among medical doctors. They see little coherent theory of the world, just a slew of results validated by clinical trials. Until you have a clinical trial to prove it, a fact falls squarely in the "unknown" category.

I once argued with a doctor about the possibility of cell phone and wifi radiation causing cancer. She couldn't even conceive of the argument I was making: infants are made of organic molecules at room temperature and we know from a large number of experiments how such molecules react to radiation. "But how do you know infants aren't more susceptible?"