Well, it’s true that “reasoning was not designed to pursue the truth. Reasoning was designed by evolution to help us win arguments.” Check out “The Enigma of Reason,” by one of my favorite contemporary philosophers, Dan Sperber.
But that fact doesn’t make authoritarianism better than democracy. If anything, it makes democracy even more necessary. At least the Democratic process can take those self serving arguments and turn them into something pro-social. In a dictatorship, they simply remain self-serving.