In The Republic where he exalted the Hellenes over the barbarian races and suggested a nation state run by Guardians who would oversee and control every facet of society from education to production including controlling domestic partnerships.

It was literally used as a blueprint to develop and justify fascism:

The cover of Hildebrandt's book left no room for doubt regarding the political sympathies of the author: it bore a swastika. In that very same year, Hildebrandt also published a translation of Plato's Republic in which he explicitly associated Plato and Hitler, presenting the latter as the philosopher guide of the dialogue. As a matter of fact, Hildebrandt's interpretation underlined many of the themes that were going to play a prominent role in subsequent Nazi propaganda and their appropriation of Plato, including an emphasis on Fuhrertum, racism, and, more specifically, eugenics.

• Towards Nazism: On the Invention of Plato’s Political Philosophy

I think this passage From Umberto Eco's Ur Fascism gets at the heart of your question and the essay itself is a fantastic read. The issue is that fascism is an inconsistent and contradictory political ideology.

Ur Fascism

Fascism became an all-purpose term because one can eliminate from a fascist regime one or more features, and it will still be recognizable as fascist. Take away imperialism from fascism and you still have Franco and Salazar. Take away colonialism and you still have the Balkan fascism of the Ustashes. Add to the Italian fascism a radical anti-capitalism (which never much fascinated Mussolini) and you have Ezra Pound. Add a cult of Celtic mythology and the Grail mysticism (completely alien to official fascism) and you have one of the most respected fascist gurus, Julius Evola.

But in spite of this fuzziness, I think it is possible to outline a list of features that are typical of what I would like to call Ur-Fascism, or Eternal Fascism. These features cannot be organized into a system; many of them contradict each other, and are also typical of other kinds of despotism or fanaticism. But it is enough that one of them be present to allow fascism to coagulate around it.