I just watched 2x03, "Save the Last One".
I gotta say, though I'm surprised Shane would do something so blatantly harmful to someone just for his own survival, I've known there was something "off" about him since early in season 1.
He's like Rick in some ways; loyal, protective and almost chivalrous with others, but in Shane's case, it's more pretense than conscious conviction or actual personality traits. And it's a pretense that often gets shed at the first sign of stress and personal turmoil, i.e. beating Ed senseless, angrily pointing his gun at Rick behind his back, shooting Otis for his own survival.
I think from here, Shane has nowhere to go but downhill. It starts with sacrificing someone else to save himself, but IMO it'll quickly spiral into much, much worse. Eventually, I think there'll be a open standoff of some sort between Shane and the others/Rick.
It kind of goes back to the discussion about how real
people would react to the situation and if their humanity would remain intact. I think, realistically, there would be people like Rick. Those would are consciously aware of the moral implications of their choices and, in a situation like Walking Dead, see the importance of remaining true to themselves and what little morality people have left.
And there'd always be the people who are first and foremost about their own survival and comfort. The plunderers.
But there'd also be the people like Shane, people who do it partially for show, and as time and stress wears on, they'd slowly allow more of their humanity to become victim to their circumstances and the stresses they carry.
All in all though, I'm really interested to see where this season is going to take us. Looking good so far.