As to the OP, I think that it doesn't draw any distinction between fanatics about zombies and apocalyptic fun and games. Also, it pejoratively names the viewpoint, which I suppose feels like an imposition instead of an invitation to discussion. I'm not sure my emphasis on these points distinguish my position and the OP so very much. I find it very hard to believe that anyone really likes to habitually play imperial stormtrooper. The helmets directly refer to German WWII helmets after all. There is a perfectly visible reference to the real Nazis right there.
As to willing suspension of disbelief, dead people who walk around are self-contradictory. Dead is dead: Only live people walk around. Zombies are only acceptable as symbolic of deeply felt fears. They are only familiar from previous movies and books, just as starships are only familiar from previous movies and books (since justification within the fiction is now deemed too taxing for the youthful mind, that is.) But anything that is self-contradictory poses more problem for willing suspension of disbelief. Only the intense interest in the real (in the mind of the zombie fanatic, that is) threat posed by the metaphor of the zombie makes it easier to suspend disbelief.
"Liking Firefly is not the same thing as believing in Dunning School history and ascribing to a Neo-Confederate world view." Obviously this is true. But this is like saying you're only a racist if you're a dues paying member of the Klan or the Nazis. It's science fiction, albeit of a deeply stupid sort, so nothing is direct or overt.
The question is the covert
racism and reaction. NeoConfederates vociferously deny that the Civil War was about slavery. The Alliance has no discernible motive. And the notion it was simple greed is specifically contradicted, it is a much more monstrous desire to change human nature. The picture of the Alliance is a hopeless mess. Except that it stands in for the North, so the viewer can apply whatever feelings he has about the North, at least until the climax where the face of the Operative both exposes the evil and the hollowness of the North's pretense to virtue.