Why won't these zombies die?

Films about zombies are now their own sub-genre of horror. Nobody has explained why zombies, which are dead and decaying, need to eat flesh. It's not like they are able to digest.

Anyway, Anne Billson wrote a good article in The Guardian about why the sub-genre is popular

Because zombies, even more than vampires, are symbols of so many of today's subconscious fears. They stand for any section of society that can be easily depersonalised for social or political reasons. They represent the great unwashed, that fearsome underclass of knife-wielding hoodies certain newspapers are always warning us about. Or they're metaphors for poverty, influxes of immigrants or refugees who (we're told) will steal our housing and jobs. They could be gangs of feral children, football hooligans or those anonymous carriers of swine flu, at first kept at a safe distance but spreading infection ever closer to home to threaten us and our communities.

At their most basic level, zombies represent anarchy, threatening to upset the established order. Whereas a decade or so ago this might have seemed undesirable, now we're not so sure, because the established order hasn't been doing us any favours lately. In fact, its representatives have taken refuge in their own version of Fiddler's Green, where they have been leading a life of hedonism, paid for by the sweat of our labours. So whereas zombies might once have been a metaphor for the dreaded underclass, the recession is a reminder that we are that underclass, those faceless masses that need to be contained lest they take bites out of the bankers and politicians.

Take a look at the footage of the G20 demos in London, which shows crowds of people herded, clubbed and beaten back by heavily armoured police. The establishment is treating people like the zombies in Romero's films - as a faceless mass, less than human, a tide of contagion to be stemmed at all cost. They are no longer just reminders of our mortality. They are us. We are all zombies now.

Interesting point Ms Billson, but why do they need to feed on the living?