In a pure democracy 51% of the people would vote to strip 49% of their voting rights. And then those 51% of the remaining voters would vote to strip 49% of the remaining voters of their voting rights, ect. until you only have two voters left, a King and a Queen.
The founders were in favor of a rights based, Locke based, government.
I suggest studying more into monarchy. Monarchy is not the equivalent of authoritarian rule; it may take the form of an authoritarian dictatorship but Republics resulting in dictatorships have historically taken the form of military or ideological rule, rather than rule based on a traditional class system.
Human nature ensures democracy results in in tyranny; if the consent of the masses is required then the masses will fall into an ideological mold and minority [opinions] will be discarded as politically inconvenient.
Jefferson read Locke but he also feared the rise of the proletarian and preferred an educated voting class; Hamilton and the Federalists were in favor of aristocracy.