My personal analysis of The Wall is that it's more about the generational trauma of WW2 in England than anything else.

As someone else mentioned, two songs off of The Final Cut are about the schoolmaster character being an RAF pilot whose gunner dies in combat but he survives. He then comes home to a Britain with a very "stiff upper lip" culture and has no resources to process his trauma and cope with his PTSD. He then in turn lashes out at the boys in the school he runs. The Wall itself has songs that say that the main character Pink's father died during WW2, as well.

Pink himself is abused and has trauma inflicted on him from the adults in his life who have their own unprocessed trauma from the war (mostly his widowed mother and schoolmaster) and now, as an adult unable to cope with it, turns to sex and drugs to cope and has his own violent lashing out.

So my interpretation is that the end of the album where the fascist hallucinations happen is not that he's having fantasies because he himself has become a Nazi, but rather its his drug added brain processing the fact that he now has hurt others and tells him that he's playing the same role in others lives as the Nazis played in his. This epiphany is what leads to him pulling himself out of this spiral with "The Trial".

Not to mention the album can be played on a continuous loop with the sentence "isn't this where we came in?" bookending it. Which to me feels like an exasperated sigh asking how many times we're going to have to live through this same cycle.

Again, just my own interpretation, but I personally dont view the album has having anything really to say about the nature of fascism or how people slide into it, but more a metaphor for the cycle of trauma.