Is there anything that you consider proven beyond any possibility of doubt by both empirical evidence and pure logic, and yet saying it triggers automatic stream of rationalizations in other people?

• Hitler had a number of top-level skills, and we could learn (some) positive lessons from his example(s).

• Eugenics would improve the human race (genepool).

• Human "racial" groups may have differing average attributes (like IQ), and these may contribute to the explanation of historical outcomes of those groups.

(Perhaps these aren't exactly topics that Less Wrong readers (in particular) would run away from. I was attempting to answer the question by riffing off Paul Graham's idea of taboos. What is it "not appropriate" to talk about in ordinary society? Politeness might trigger the rationalization response...)