Im Ah-joo
I'm not one, but I think the whole underlying theme to the virus suddenly being present in everyone is that it's trying to stress that we're all animals when you strip everything away. Once the brain, the human part of us, is shut down we're reanimated with one of the basic survival instincts of any predator: kill and eat.
Any other theories of what they're trying to tell us?
No I disagree with this :"underlying theme to the virus suddenly being present in everyone is that it's trying to stress that we're all animals when you strip everything away". The main driving point to this show is how a group of survivors will survive not only the apocalypse but each other. Although, this added twist of everyone being infected will definitely have an imapct on the group. It'll fuel the fear that all the survivors have now that they know that hope is really lost for the moment. No matter how long they survive they will still face death and in death they will become the monsters they've been so determined to outlive. It really is a great spin on the zombie genre. They are now left with the disheartening fact that everyone is doomed to become a walker. I can only imagine what such a notion will have on the group, well at least what is left of them, in the finale.
And as far as the rest of your theory goes when the brain is reanimated as shown by Jenner it seems that only the lower most portions of the brain is functioning. That does support the basic drives theory, but the writers are missing some key components that would reawaken within those centers. That and I don't think the writers are trying to highlight the fact that humans are animals. If they were this show would be very dull. The main power for this subplot will be to only bring the group down more. Why keep fighting if you're bound to become one of them?
For this show, and as a psych major, I have more fun analyzing the characters and their various personalities. Such as Shane, his slow downward spiral was intriguing, and began long before this past episode. He couldn't handle the fact that his view of "right" wouldn't always be supported and in most cases it would be challenged. Even if his view was in fact the better choice. He had a high need for power, which left him constantly vying for control.
Possible Spoiler (highlight): Of course his ultimate downfall came at the hands of Lori and her constant need to feel protected/secure.
As a side note : You should rethink the topic title of your thread. I find this show fun to watch even with its various continuity issues. I wouldn't try to over-analyze a work of fiction either. it's pretty nice to suspend that disbelief for an hour every sunday xD