Zombie Cliché Lookout:
The freak out is an essential part of a lot of genre entertainment, from the nervous private getting his first taste of war, to exhausted survivors trying to cope with some cataclysmic disaster. Zombies take this trope and turn it up a few notches. Survivors don’t just have to deal with the horrors of gore, death, destruction, and cannibalism, they have to personally destroy monsters who were, only a short time ago, acquaintances and loved ones. And if they don’t, they’re going to be eaten alive.
The psychological stress on everyone is more than understandable, but it’s often condensed into one or two designated freak out characters. A prime example of this being Hudson from Aliens. Sure, all the rest of the civilians and colonial marines were scared, but only Hudson vocalized it.