I don't know, it seemed to me that Hershal DID change a bit when Shane was making his point - ie, he shot her (the first zombie he shoots) right in the chest multiple times, in the heart, lungs, etc. A person would normally be dead in that instance, but she kept on going like nothing happened. The look on Hershal's face to me said that he finally "got it", even if he didn't WANT to believe it.
I also thought this was a great episode, redeeming any of the slow/soap-opera elements of some of the earlier episodes.
And, after getting over the initial shock of the end of the episode, I started to wonder about Sophia being in the barn. Did Hershal know she was in there? I mean, they are the ones who corralled the zombies in there right (Hershal's group)? So, the events are: they put a 10 year old girl zombie (or, infected person) in the barn. A day or two later, a bunch of strangers come in telling them that they're looking for a 10 year old girl lost in the woods nearby. Do you think he knew and was hiding it?