Here's the Miriam-Webster definition of
fas·cism
Pronunciation: \ˈfa-ˌshi-zəm also ˈfa-ˌsi-\
Function: noun
Etymology: Italian fascismo, from fascio bundle, fasces, group, from Latin fascis bundle & fasces fasces
Date: 1921
1 often capitalized : a political philosophy, movement, or regime (as that of the Fascisti) that exalts nation and often race above the individual and that stands for a centralized autocratic government headed by a dictatorial leader, severe economic and social regimentation, and forcible suppression of opposition
2 : a tendency toward or actual exercise of strong autocratic or dictatorial control <early instances of army fascism and brutality — J. W. Aldridge>
So if you want to talk about Science Fiction movies that show societies with those qualities, go ahead.
That's a pretty simplistic definition that doesn't actually attempt to distinguish it from, say, Stalinism.
That's part of the issue with fascism. Like I said, it's most obvious factor is the totalitarian, dictatorial element (although I suppose you could have a fascist junta too). But the more hazy element is the bit about "economic regimentation." What the HELL is that supposed to mean? The soviets were "economically regimented" as are Scandinavian socialists if you want to think of it that way. What's the difference between the two, because I doubt anyone would call the soviets fascist.
Again, the problem with all this type of discussion is that the words become shorthand descriptors for what we see, as distinct from the political science definition. I mean, ostensibly, Argentina was a Democracy during the Falklands War, even if it was actually controlled by a military junta at the time. So was it a democracy? A fascist state? A dictatorial military junta propped up by capitalist industrialist institutions who were free to do as they pleased?
Likewise, Franco was ostensibly a fascist, but his economic policies changed during the course of his reign, and weren't the same as those of, say, Hitler.
At any rate, I think that for the most part, sci-fi governments usually fall into one of three categories:
1.) "The utopian free universe", like "The United Federation of Planets" or some other similar democratic, liberal (in the sense of personal liberties, not "left-leaning") government, usually with some kind of legislative branch and an executive leader of some sort (president, chancellor, etc.).
2.) The "Nazi Germany" clone. Degree of similarity may vary.
3.) The "Imperial Rome" clone. Again, degree of similarity to the actual historical Roman empire will vary.
Sometimes you get outliers, of course. Frank Herbert's first Dune novel is pretty much the Italian Renaissance version of history, except united by an emperor. Once in a while you see "Victorian England in Spaaaaaaace", too. But for the most part, your biggies are your nazi clones, your roman clones, and your U.N. one-world-government clones.
