That's the very reason we built checks and balances into our government. To constrain it from ever having the "unfettered" power you're describing. From multiple competing branches of government to the Bill of Rights, we codified these restraints to contrast with the absolute power of the monarchies that had come before. Our democratic principles themselves are a restraint on the power of authority; if someone does something we don't like we, the people, vote them out. I support most forms of democratic reforms like Initiative, Referendum, and Recall which you can see the clear historical progression of through the Western states.
None of this has anything to do with the discussion of how to run the economy. There have been authoritarian capitalist monarchies, authoritarian socialist oligarchies, authoritarian feudalist collectives, and authoritarian slaver states. And just about every mashup of the above and others not mentioned. What none of us want is totalitarian/authoritarianism, regardless of what guise it's cloaked in. Being capitalist didn't save Japanese Americans from the internment camps in WWII. What matters are the specific actions, not any of these ideological labels we bandy about.