Friend or Foe

ok so I woke up last night from a weird dream. I don't remember much except for the fact that there where some freaking zombies in it.
Now this got me to thinking about well you guessed it zombies. my first thought was wait a minute I just found a giant plot hole in one of my favorite comics The Walking Dead. It is an uber long story about a world overtaken by zombies and it focuses on a small group and their attempts to make some semblance of a normal life within it. The hole I found was zombies are undead if I am not mistaken. Their flesh is rotting as their bodies are dead, it is only the brain which seems to still be functioning. If this is the case what keeps the humans in the story from just completely rotting away in like 6 months. I mean they just have to keep hiding out in the jail they have found until all the zombies just turn into worm food. Of course this doesn't seem to be the case. So my question for everybody is "what keeps them from just rotting away". The theory that I am going on is that because the brain is still functioning it must still be keeping some of the other bodily functions alive as well.

On another note if zombies start to show reasoning skills such as in land of the dead then have they actually lost their humanity and are only acting on instinct or is there some aspect of their humanity that survives. If their essential humanity is struggling and under attack from this "zombie" virus or whatever is it our duty to help them regain their humanity instead of just killing them all outright.