Zombies, at least, have the whole suprise thing going for them. With zombies, people don't see a flesh eating monster, they see a person stumbling along who might be injured. Most normal people would stop and try to help, then it's "Hey, maam, are you alri-AAAAAIIEEE you BIT me you crazy b***h!" By the time anyone realizes what's going on, the infection has spread and the damn things are everywhere.
Ha, good point. Until the word gets out, zombies work because people do not expect others to behave that way. Nor do they expect large numbers of zombies to go around, breaking into houses and such. Modern homes are secure, not due to physical security, but because society provides for police and stability.
The little girl zombie in "Dawn of the Dead" got the jump on the guy in the beginning because why would two adults be worried about a little girl that they knew?
Welcome to the board.