The number one problem with zombies, as far as I’ve seen them depicted, is that they’re a short term threat. I’m not talking about the type of zombies in 28 Days Later, where people just get a virus and become dicks, I’m talking about genuine, shambling, ambulatory corpses seeking BRAAAIINS (or zombie cattle seeking GRAAAIIINS).
I’m not saying they wouldn’t be an existential threat–far from it. A zombie apocalypse would not be a pleasant experience, but it would eventually end, with survival favoring those in certain climates and locales.
First off, if the zombies are rotting corpses, then simple human decomposition would ensure the zombie throng would quickly burn out in about 18 months. They simply wouldn’t be able to walk after a certain period of time, as their muscle tissue and tendons deteriorated to the point that they simply stopped moving.
So, if you find yourself in a sparsely-populated area when the zombie balloon goes up, you just need to hold out for about 18 months and you’re pretty much good to go. But it gets better! If you’re in a tropical or humid location, the zombies will decompose at a far faster rate. You might only need to hold out for only a year if you’re in the Southeast US.
But if you’re in more northern climes, you’re not in that bad a situation, either. If the zombie throng starts shuffling in earnest in the spring or summer, you’re in for some tough times, but once winter hits, freezing temperatures will slow or completely stop the undead, allowing you to gather head shots at will.
So, best case scenario, you’ve gotta hold out for only 6 brief months–a hockey season. Worst case, you need only endure 18 months, with the zombie contingent steadily reducing in number with each passing week, before dropping off exponentially after about 13-14 months. That’s why the zombie apocalypse is the least terrifying end-of-the-world scenario. If a big asteroid hits the earth, we’re all fucked, with any survivors leading a life of extreme starvation and savagery as they slowly die off. A supervolcano eruption leaves us with a similar scenario. Global thermonuclear war dispenses with the whole, drawn-out death of a species and just knocks us all out fairly quickly.
In light of actual, real-world apocalyptic options, the zombie plague is actually the preferable one. It offers a real good chance for survival of the species and a chance to quickly recover. Unless, of course, the impetus for the zombie plague is a biological agent that infects everyone (like in The Walking Dead), expressing itself not only when bitten and infected by a zombie, but also upon death (even a non-zombie-inflicted death). In that case, game over humanity. Just try to infect as many animals as possible, because zombie grizzlies would be really cool to see.