^^ I think Daryl has years of reasons to turn against Merle.
As for Glen, he was not a sucker. His behavior was consistent with what the average person would do in that situation.
Did anyone else notice how after Darryl had pulled Carol's knife out of the walkers face and wiped the goo off he held it up against the wound as though he was gonna stab it.
I think he was figuring out the angle at which Carol had stabbed the thing and the what way she would have gripped the knife and came to the conclusion that since the knife was buried into the things face practically to the hilt bringing her arm right up against its mouth without having killed it that there was no way she wouldnt have gotten bit which ties into a lot of peoples interpretation of Darryl sitting alone in the corridor angrily stabbing the floor and walls as him expecting to find a zombified Carol behind that door and had sent the others away whilst he himself up to the job of killing her.
That sounds about right to me.