alt Hacker NewsThe Open Society and Its Enemies is an important and interesting anti-authoritarian book. Unfortunately, from a purely Plato-scholarship/interpretation perspective, it's trash.
Just read the Republic and see for yourself. Kallipolis is, first and foremost, simply meant to be a metaphor for the organization of an individual's soul. Second, the suggestion that the city should be led by a caste of authoritarian Philosopher Kings is given inside of a conditional---the condition being: those leaders must be True Philosophers; where True Philosophers know the Good and thus know (in a nearly omniscient-like way) what is best for everyone (and act accordingly). It is left wide open whether such True Philosophers even exist, thus it is left wide open whether such a social organization would ever work in reality.
Plato's other political dialogues, like Statesman and The Laws, are much much less utopian and "authoritarian" and deal with very practical political issues. It would be weird to be an authoritarian utopist and then go and write dialogues like those.
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In The Laws you find: strict supervision of marriage age, mandatory procreation windows, state monitoring of reproduction, penalties for bachelors, public scrutiny of household conduct, drinking regulation, limits on wealth and inheritance, formal theology enforced by law, criminal penalties for impiety, special prisons for “atheists”, etc. it goes on and on. The Laws makes The Republic look like Disneyland to be honest.
Comment approved by my wife, who is a Plato scholar. Your point that whether True Philosophers even exist is left open is the kind of problem she points out all the time in dogmatic interpretations. It sounds basic, but it's so important to keep in mind that just because a character says something (even if that character is Socrates), that doesn't mean it's the "view" of the dialogue. And you have to be careful to pin down exactly what is being claimed, as you point out with the conditional. Plato is a master (surely one of the greatest of all time) of creating a dynamic space to think in without settling the questions raised.