zombie lifestyle deemed unsustainable

That's totally the thing about zombies - once the outbreak happens, it's an exponential decay. See, as a zombie, you go out and eat someone. And after a (reportedly) horrific few moments or minutes, dude dies. And then awakens to find himself a zombie brethern. Who is hungry. Who wants to eat him some live brains. So in your own state of insatiable hunger, you've not only exhausted a food source, but you've also created competition for other food sources, sources that are finite in number.

And then what? What about when we're All zombies? Then just aimless wandering, clutching our stomachs (if they're still there, right? Like if Beth from next door didn't eat it before turning you into a zombie, or if you're not someone who unfortunately died about 2 months ago and had to dig yourself out of the ground, only to find your stomach had decayed. Anyway), complaining about the lack of brains - FOR EVER?

(Above: Sarah Polley says, "No!") That would suck.

And that's why we should try to keep an eye out for any signs of zombification before they really get out of control, you know?