The issue with me, is that the writers HAVE to automatically assume that people in general are too stupid to live if Zombies can actually be a threat. Zombies are in general a stupid premise. Let's ignore all the obvious and mostly external biological reasons that zombies wouldn't exist.
First off, what makes us the top of the food chain is that combined with our ability to think sideways, adapt the world to us, and our instinct of self-preservation that doesn't force us into mindlessness, we are the preeminent killers on this planet. We may not have the natural tools, but we've designed a whole slew of artificial ones that kill faster, effectively and more efficiently than any other species in this world. Not to mention that our cities are designed to make it difficult for our enemies (namely other living, thinking, planning humans) to navigate, making them excellently defensive fortresses.
Now, take zombies, which is a human with no sense of self-preservation, no thought beyond 'eat brains' and definitely no tactical thinking capacity. For heaven's sake, they can't even figure out a bloody DOOR KNOB!
Which makes me wonder how stupid the entire race of humans has to be if they can't clean up that mess in less than a week.
Shows like the Walking Dead would be better served by making the 'monsters' a little less common but a bit more dangerous. Instead whenever I see people dying to zombies, I nod to myself, thinking 'Yep, that's about right, if you aren't smart enough to know how to deal with a mindless creature.'