Our sense of the realistic (cf Eastenders, Bicycle Thieves, the work of Posy Simmonds, etc) is the result of our training in the bourgeoise capitalist realism which is a part of the ideology of capitalism (whose purpose was to dismiss the monstrously - mystical - mythical - religiosity which was such a part of the ideology of agriculturalism/aristocracy: cf The Lutteral Psalter).
The appearance of these tropes in the culture of capitalism is never a good sign as the hideous stumbling metaphor of the zombie shows us so clearly. That the modern zombie is the proletariat needs no explanation (the line from the consumers of Dawn of the Dead to the shop-workers and game show contestants of Shawn of the Dead is written in the brightest light) but what is interesting is that in a zombie horror it is the zombie that is real.
The 'realistic' of these texts (with its ekphrastic detail of daily life turned upside-down and the world-around-us in-ruins and the now standardised [in the sense of the culture industry] tightly woven discourse of realism) is the reality of bourgeois capitalist realism that Flaubert (et al) and later the cinema wrought upon the world. The realistic is the ideological and the monster is (on the contrary) very real indeed.
Just as the morlock (which is the true original of the modern zombie not the voodoo zombie of the first wave of Hollywood zombie films) was the proletariat as warning ('exterminate all the brutes' is the cry of Wells as much as of Kurtz) so is the zombie. The zombie is the working-class, the poor, the excluded (it almost isn't a metaphor at all) and as such is the most real thing in zombie horror texts. The zombie is not how the working-class are treated in fiction rather it is an accurate depiction of how the weakest factions of the working-class live in society right now and the methods (murder mainly) that must be used to 'deal' with 'them'.
We must recognise that the figure of the sheriff which closes the narrative of Night of The Living Dead is the same as the sheriff who opens the story of The Walking Dead: only now (neo-managerially) he no longer chews tobacco.