I think he's going after shock, but only insofar as to show how messed up everyone becomes in this situation. Maggie's decision, the direction the twin boys go, and how hardened Carl is becoming, it's all down to "yeah, if the world ends, it's going to be hard to keep it together."
I keep going back to McCarthy's The Road as a parallel to this story. They're both father/son stories about how far we'll go to protect our offspring, convinced that the world is horrible, even as they grow up knowing no other world. However, I wouldn't put it past Kirkland to take that away in the end, though I believe if Carl dies, it would be the end of Rick.