I gotta give this episode a 10, I think it is probably the best episode this season. The moment with Rick and Carl just mowing down zombies left and right with Ak's was just fucking awesomely badass! Thats the kind of father son bonding that I want to see during the Apocalypse
Carl saved Rick's ass once again and is proving that he is the John Conner of the Walking Dead!
To answer the question of why the guy wanted to be locked in with a person that was about to turn is I think because that was his son and he just didn't want to leave his kid. I can understand that, he probably figured if his son was gonna die he might as well go ahead and die anyways, what does he have left to live for kinda thing.