First of all everyone uses the term Zombie wrong.
Zombie is a term given to a victim that was given a potion by a Bokor. This potion usually contains the poison of a blow fish. The person's pulse is so weak that doctors and even the medical machines were fooled into thinking the person was dead. Then the night after the person had been buried the bokor would dig up the victim's grave and give them another potion that would make them mindless and easier to control.
What everyone is referring to is actually a reanimated corpse.
Secondly yes it is possible for people to be helpless against reanimated corpses:
1.) As a society we have become desensitized to it. Movies, shows and even books on the subject are coming out more than ever. People going to haunted houses on halloween, dressing like the dead on halloween.
So if the dead rose, people would be so desensitized that by the time they realize its not an actor and actually one of the dead it would be too late.
2.) Paralyzed with fear. Some people could have too high of an adrenaline rush that they can become paralyzed an unable to move. Even fear can have a profound effect on people, because they go in shock and cannot believe what is happening.
3.) Technology. Just because technology has improved and help benefit society does not mean it cannot be our greatest enemy. We are studying and playing around with Diseases, DNA, making clones and even people are beginning to clone their pets and THINK that their cloned pet will have the same personality and every trait their deceased pet had. Actually those that have cloned their pet have stated their clone of their pet is nothing like their previous animal at all. They act like its shocking when of course it would not be like your previous pet.
Destroying nature's habitats and a lot of things are changing in our environment.
4.) Weight. Taylor here posted that as a society we have gained weight and it is something that can make us sitting ducks. Very true.
Etc. . .That is why there are so many movies, shows and books about it. People fear things that are the unknown. We do not know how these things would be like. Would they remember anything from their life? Could they talk? Or would they just go around infecting/killing those that are still alive? Reanimated corpses are talked about in many mythologies around the world. Every culture had beliefs about how to stop the dead from rising from their graves. In-fact these reanimated corpses that are incorrectly identified as zombies could in-fact be vampires. The original vampires, NOT the hollywood-dracula vampire, but the actual vampire. Its quite possible that is what it is. The dead rises from the grave, bites people and infects them, both are dead, etc. . Many similarities.