1. scope creep. They will slowly become more authoritarian over time: (legitimate) authority in one area will bleed into (illegitimate) authority in another area.
2. they will be unable to deal with defiance. Because they're not used to it and because to much of their identity is intertwined with their professional authority.
There are too many people out there who enjoy exercising their power over others. Too many teachers who completely lose it when students pull some harmless prank. Too many police officers who threaten violence when talked to disrespectfully. The victims of overreaching authority are always -- as the article points out -- the weaker members of society. Standing idly by in the face of injustice is not the mature adult thing to do; it's plain cowardice.
All authority should be assumed to be illegitimate, and structures of authority that cannot justify their existence must be dismantled.
Why should I?
(Old school PLIF ref :) https://imgur.com/LBrFO )
-MLK, Letter From a Birmingham Jail
Put it this way: Many people who history currently regards as being "correct" were assholes, and many people who history currently regards as being despots were wonderfully charming and pleasant.
Also, the view of these people over the course of history has changed (due to many things, some ranging from societal change of opinion to historical revisionism).
As stated in the article: "Cartwright described a related psychiatric disease, dysaesthesia aethiopica, that he said was ‘the natural offspring of negro liberty – the liberty to be idle, to wallow in filth, and to indulge in improper food and drinks’. It’s easy to roll our eyes at such shoddy logic and obvious racism. But to many Southern whites, Cartwright’s explanations made perfect sense. They were used to justify both the murder of slaves and the recapture of runaways."
Was Cartwright being an asshole? Or were the slaves trying to escape being assholes? Any person's opinion is unfortunately defined by personal circumstance, society, and interest.
I'm pretty sure that James F. Blake thought Rosa Parks was just being "an asshole".
I am reminded of this quote from G.B. Shaw: "The reasonable man adapts himself to the conditions that surround him... The unreasonable man adapts surrounding conditions to himself. All progress therefore depends on the unreasonable man."