Rational thinking is, at it's core, an aesthetic exercise
Rational thinking, at its core, is an aesthetic exercise—not a moral, practical, or logical one. Nazi and Enlightenment thinkers alike were motivated by the beauty of their ideas. How else would you miss the irony of creating a country founded on both freedom and slavery? How else would you premise the creation of a master race on the annihilation of the most intelligent people in your country?
Morality would find those ideas repulsive. Practicality would find them expensive. It's only in beauty that paradoxes are permitted. Consider the Japanese. How else would you go from being a people who, in the first half of the twentieth century, conducted bioweapons experiments on humans, to being renown in the second half for social programs for the elderly, low crime rates, and overall politeness? This is the same country that has the highest return rate for misplaced wallets. Why do the Japanese do this? Is it because it's the right thing to do? Or is it because it's the most elegant?