Starship Troopers was heavy on the fascism.
You need to re-read it. Or your opinion was biased by the deplorable Paul Verhoven movie adaptation.
The "Federation" was a worldwide democratic republic with universal civil rights. The only real limitation on everyone was that the voting franchise an the right to run for public office was
earned. RAH didn't get too deeply into it, but the service to earn the voting franchise was varied, and they'd even tailor it for disabled people etc.
(Note that our own U.S. Constitution does not explicitly spell out what criteria granted the right to vote either...)
And those who were serving to earn voting rights were unable to vote or hold office until their service was complete. The military was subordinate to the civilian government. Military service was completely voluntary etc.
The book was very heavy on themes of personal responsibility, and the relationship between the individual and the state and the duties of one to the other, but it was hardly fascist in any sense of the word.
I'd say that's a common misunderstanding. SST doesn't really endorse any kind of political view, it's intended to be a novel about the mindset of military men (providing an idealized representation of that, of course).
Esprit de corps, and military discipline, and the development of leadership qualities was a theme of the book, but it was a background for the political ideas RAH had.
